/* AGI 学习笔记 — site styles
   Palette note: the ink-blue and ember below are the exact two colours the
   generated SVG figures use, so figures sit in the page as native elements
   rather than as pasted-in pictures. Ember is rationed: section numbers,
   active nav, live badges. Nothing else. */

/* ---------------------------------------------------------------- tokens
   The site is black and white: the design language is the night sky behind it
   (static/sky.js), large quiet type and hairlines. Dark is the site's own look;
   light is the pinned alternative, the same page in daylight. */
:root {
  color-scheme: dark;
  --paper:      #000000;
  --panel:      #0B0B0B;
  --ink:        #F0F0F0;
  --ink-soft:   #D8D8D8;
  --muted:      #A4A4A4;
  --faint:      #707070;
  --rule:       #1F1F1F;
  --rule-soft:  #161616;
  --link:       #FFFFFF;
  --link-hover: #FFFFFF;
  --ember:      #DCDCDC;
  --ember-bg:   rgba(255, 255, 255, 0.07);
  --code-bg:    #111111;
  --mark:       rgba(255, 255, 255, 0.16);
  --shadow:     none;

  --sans: -apple-system, BlinkMacSystemFont, "Inter", "Segoe UI", Helvetica, Arial, sans-serif;
  --serif: var(--sans);
  --cjk: "PingFang SC", "Hiragino Sans GB", "Source Han Sans SC",
         "Noto Sans CJK SC", "Microsoft YaHei", sans-serif;
  --mono: ui-monospace, "SF Mono", "Cascadia Code", "JetBrains Mono", Menlo, monospace;
  --body: var(--sans), var(--cjk);

  --side-w: 272px;
  --rail-w: 208px;
}
:root[data-theme="light"] {
  color-scheme: light;
  --paper: #FFFFFF; --panel: #FAFAFA; --ink: #0A0A0A; --ink-soft: #333333;
  --muted: #6B6B6B; --faint: #9A9A9A; --rule: #E6E6E6; --rule-soft: #F0F0F0;
  --link: #000000; --link-hover: #000000; --ember: #111111;
  --ember-bg: rgba(0, 0, 0, 0.06); --code-bg: #F3F3F3;
  --mark: rgba(0, 0, 0, 0.10);
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
}

*, *::before, *::after { box-sizing: border-box; }
* { margin: 0; }

html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; scroll-padding-top: 5rem; }
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: .01ms !important; transition-duration: .01ms !important; }
}

body {
  background: var(--paper);
  color: var(--ink);
  font-family: var(--body);
  font-size: 17px;
  line-height: 1.72;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

a { color: var(--link); text-decoration-thickness: 1px; text-underline-offset: 2px; }
a:hover { color: var(--link-hover); }
:focus-visible { outline: 2px solid var(--ember); outline-offset: 2px; border-radius: 3px; }

.skip {
  position: absolute; left: -9999px; top: 0; z-index: 100;
  background: var(--panel); padding: .6rem 1rem; border-radius: 0 0 6px 0;
}
.skip:focus { left: 0; }

/* ---------------------------------------------------------------- topbar */
.topbar {
  position: sticky; top: 0; z-index: 40;
  display: flex; align-items: center; gap: .75rem;
  height: 52px; padding: 0 .85rem;
  background: color-mix(in srgb, var(--paper) 86%, transparent);
  backdrop-filter: saturate(1.4) blur(10px);
  border-bottom: 1px solid var(--rule);
}
.topbar-brand { font-weight: 700; letter-spacing: -.01em; color: var(--ink); text-decoration: none; }
.topbar-right { margin-left: auto; display: flex; align-items: center; gap: .3rem; }
.repo-btn { color: var(--ink-soft); text-decoration: none; }
.repo-btn:hover { background: var(--rule-soft); color: var(--ink); }

.icon-btn {
  display: grid; place-items: center; width: 34px; height: 34px;
  background: none; border: 1px solid transparent; border-radius: 7px;
  color: var(--ink-soft); cursor: pointer;
}
.icon-btn:hover { background: var(--rule-soft); color: var(--ink); }
.i-moon { display: none; }
.i-sun { display: none; }
.i-moon { display: block; }
:root[data-theme="light"] .i-sun { display: block; }
:root[data-theme="light"] .i-moon { display: none; }

.lang-btn, .lang-inline {
  font-family: var(--sans); font-size: .74rem; font-weight: 600;
  letter-spacing: .06em; text-transform: uppercase; text-decoration: none;
  color: var(--ink-soft); border: 1px solid var(--rule); border-radius: 6px;
  padding: .3rem .55rem;
}
.lang-btn:hover, .lang-inline:hover { border-color: var(--ember); color: var(--ember); }
.lang-btn.disabled, .lang-inline.disabled { opacity: .35; pointer-events: none; }

.lang-btn:focus-visible { outline: 2px solid var(--ember); outline-offset: 3px; }

/* ---------------------------------------------------------------- shell */
.shell {
  display: grid;
  grid-template-columns: var(--side-w) minmax(0, 1fr) var(--rail-w);
  gap: 0 2.5rem;
  max-width: 1420px;
  margin: 0 auto;
  padding: 0 1.5rem;
  align-items: start;
}

/* ---------------------------------------------------------------- sidebar */
.side {
  position: sticky; top: 52px;
  height: calc(100dvh - 52px);
  overflow-y: auto; overscroll-behavior: contain;
  padding: 1.6rem .5rem 3rem 0;
  border-right: 1px solid var(--rule-soft);
  scrollbar-width: thin;
}
.brand { display: flex; gap: .7rem; align-items: flex-start; text-decoration: none; color: var(--ink); }
.brand-mark { color: var(--ember); flex: none; margin-top: 2px; }
.brand-text b { display: block; font-size: 1.06rem; letter-spacing: -.01em; line-height: 1.3; }
.brand-text i {
  display: block; font-style: normal; font-size: .78rem; line-height: 1.45;
  color: var(--muted); margin-top: .12rem;
}

.search { position: relative; margin: 1.15rem 0 .4rem; }

.side-nav { margin-top: 1rem; }
.nav, .nav ul { list-style: none; padding: 0; }

/* topic groups -------------------------------------------------------- */
.nav .grp + .grp { margin-top: .1rem; }
.nav details > summary {
  display: flex; align-items: center; gap: .45rem;
  padding: .36rem .5rem .36rem .28rem;
  border-radius: 6px; cursor: pointer; user-select: none;
  list-style: none;
  font-family: var(--sans); font-size: .715rem; font-weight: 650;
  letter-spacing: .085em; text-transform: uppercase; color: var(--muted);
}
.nav details > summary::-webkit-details-marker,
.nav details > summary::marker { display: none; content: ""; }
.nav details > summary:hover { background: var(--rule-soft); color: var(--ink); }
.nav details[open] > summary { color: var(--ink); }
.nav details > summary .chev {
  flex: none; color: var(--faint); transition: transform .16s ease;
}
.nav details[open] > summary .chev { transform: rotate(90deg); color: var(--ember); }
.grp-name { flex: 1; }
.grp-count {
  font-family: var(--mono); font-size: .655rem; color: var(--faint);
  font-variant-numeric: tabular-nums; letter-spacing: 0;
}
.grp-body { padding: .3rem 0 .55rem .1rem; }
/* a group holding the current page keeps a quiet marker even when scrolled */
.nav details:has(a.active) > summary .grp-name { color: var(--ink); }

.nav .sec { margin-bottom: .8rem; }
.grp-body > .sec:last-child { margin-bottom: .1rem; }
.sec-num {
  font-family: var(--mono); font-size: .68rem; color: var(--ember);
  font-variant-numeric: tabular-nums; margin-right: .4rem;
}
.sec-name {
  font-family: var(--sans); font-size: .685rem; font-weight: 600;
  letter-spacing: .06em; color: var(--muted);
}
.nav .sec > ul { margin-top: .28rem; }
.nav .sec > ul > li > a {
  display: block; padding: .22rem .55rem .22rem .7rem;
  font-size: .875rem; line-height: 1.45; color: var(--ink-soft);
  text-decoration: none; border-left: 2px solid transparent; border-radius: 0 5px 5px 0;
}
.nav .sec > ul > li > a:hover { color: var(--ink); background: var(--rule-soft); }
.nav .sec > ul > li > a.active {
  color: var(--ink); font-weight: 600;
  border-left-color: var(--ember); background: var(--ember-bg);
}

.side-foot {
  margin-top: 1.8rem; padding-top: .9rem; border-top: 1px solid var(--rule-soft);
  display: flex; align-items: center; gap: .6rem;
  font-family: var(--sans); font-size: .78rem;
}
.side-foot a { color: var(--muted); text-decoration: none; }
.side-foot a:hover { color: var(--ink); }
.side-foot .lang-inline { margin-left: auto; }

/* ---------------------------------------------------------------- rail */
.rail { position: sticky; top: 52px; padding: 2.4rem 0 3rem; }
.rail-inner { max-height: calc(100dvh - 6rem); overflow-y: auto; scrollbar-width: thin; }
.rail-title {
  font-family: var(--sans); font-size: .68rem; font-weight: 650;
  letter-spacing: .1em; text-transform: uppercase; color: var(--muted);
  margin-bottom: .55rem;
}
.toc ul { list-style: none; padding: 0; border-left: 1px solid var(--rule); }
.toc li a {
  display: block; padding: .2rem 0 .2rem .7rem; margin-left: -1px;
  border-left: 2px solid transparent;
  font-size: .8rem; line-height: 1.4; color: var(--muted); text-decoration: none;
}
.toc li.l3 a { padding-left: 1.4rem; font-size: .765rem; }
.toc li a:hover { color: var(--ink); }
.toc li a.active { color: var(--ember); border-left-color: var(--ember); }

/* ---------------------------------------------------------------- prose */
main { min-width: 0; padding: 2.1rem 0 4rem; }
.prose { max-width: 45rem; }

.prose h1 {
  font-size: 2rem; line-height: 1.24; letter-spacing: -.02em; font-weight: 700;
  text-wrap: balance; margin-bottom: 1.4rem;
}
.prose h2 {
  font-size: 1.32rem; line-height: 1.35; letter-spacing: -.012em; font-weight: 700;
  margin: 2.6rem 0 .8rem; padding-top: .9rem; border-top: 1px solid var(--rule-soft);
  text-wrap: balance;
}
.prose h3 {
  font-size: 1.05rem; font-weight: 700; letter-spacing: -.005em;
  margin: 1.9rem 0 .55rem;
}
.prose h4 { font-size: .95rem; font-weight: 700; color: var(--ink-soft); margin: 1.4rem 0 .4rem; }
.prose p { margin: 0 0 1.05rem; }
.prose > p:first-of-type { font-size: 1.06rem; color: var(--ink-soft); }

.prose ul, .prose ol { margin: 0 0 1.1rem; padding-left: 1.35rem; }
.prose li { margin-bottom: .35rem; }
.prose li > ul, .prose li > ol { margin: .35rem 0 .2rem; }
.prose li::marker { color: var(--faint); }

.prose blockquote {
  margin: 1.3rem 0; padding: .1rem 0 .1rem 1.1rem;
  border-left: 3px solid var(--rule); color: var(--ink-soft);
}
.prose hr { border: none; border-top: 1px solid var(--rule); margin: 2.4rem 0; }

.prose strong { font-weight: 700; }
.prose mark { background: var(--mark); color: inherit; padding: 0 .15em; border-radius: 2px; }

/* -------- curriculum --------------------------------------------------- */
.curriculum-hero {
  display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: .7rem;
  margin: 1.5rem 0 1.8rem;
}
.curriculum-hero > div,
.lab-matrix > div {
  padding: .95rem 1rem; border: 1px solid var(--rule); border-radius: 11px;
  background: var(--panel); box-shadow: 0 7px 22px -20px rgba(20, 24, 30, .55);
}
.curriculum-hero strong,
.lab-matrix strong { display: block; margin: .55rem 0 .25rem; font-size: .94rem; line-height: 1.4; }
.curriculum-hero p,
.lab-matrix p { margin: 0; color: var(--muted); font-size: .82rem; line-height: 1.55; }
.level-chip {
  display: inline-flex; font-family: var(--sans); font-size: .61rem; font-weight: 750;
  letter-spacing: .09em; text-transform: uppercase; padding: .13rem .4rem;
  border: 1px solid var(--rule); border-radius: 999px;
}
.level-chip.core { color: var(--link); background: color-mix(in srgb, var(--link) 8%, transparent); }
.level-chip.deep { color: var(--ember); background: var(--ember-bg); }
.level-chip.lab { color: #397047; background: rgba(63, 125, 84, .09); }

.learning-path {
  position: relative; display: grid; grid-template-columns: repeat(5, minmax(0, 1fr));
  gap: .45rem; margin: 1.35rem 0 1.8rem;
}
.learning-path::before {
  content: ""; position: absolute; left: 8%; right: 8%; top: 1.04rem;
  border-top: 1px solid var(--rule); z-index: 0;
}
.learning-path a {
  position: relative; z-index: 1; display: flex; flex-direction: column; align-items: center;
  text-align: center; color: var(--ink); text-decoration: none; padding: 0 .22rem;
}
.learning-path span {
  display: grid; place-items: center; width: 2.1rem; height: 2.1rem; border-radius: 50%;
  background: var(--panel); border: 1px solid var(--rule); color: var(--ember);
  font: 700 .67rem var(--mono); transition: border-color .15s, transform .15s;
}
.learning-path a:hover span { border-color: var(--ember); transform: translateY(-2px); }
.learning-path strong { margin-top: .48rem; font: 650 .78rem/1.3 var(--sans); }
.learning-path small { margin-top: .23rem; color: var(--muted); font: .7rem/1.4 var(--sans); }

.curriculum-grid {
  display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: .75rem;
  margin: 1.3rem 0 1.7rem;
}
.curriculum-card {
  display: block; min-height: 11rem; padding: 1rem 1.05rem;
  border: 1px solid var(--rule); border-radius: 11px; background: var(--panel);
  color: var(--ink); text-decoration: none !important;
  transition: transform .16s ease, border-color .16s ease, box-shadow .16s ease;
}
.curriculum-card:hover { transform: translateY(-2px); border-color: color-mix(in srgb, var(--link) 55%, var(--rule)); box-shadow: var(--shadow); }
.curriculum-card .card-step {
  font: 700 .62rem/1 var(--mono); letter-spacing: .08em; text-transform: uppercase; color: var(--ember);
}
.curriculum-card h3 { margin: .65rem 0 .35rem; font-size: 1rem; }
.curriculum-card p { color: var(--muted); font-size: .84rem; line-height: 1.55; margin-bottom: .65rem; }
.curriculum-card b { font: 650 .74rem var(--sans); color: var(--link); }
.curriculum-grid .curriculum-card:last-child:nth-child(odd) { grid-column: 1 / -1; min-height: 0; }

.lab-matrix { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: .75rem; margin: 1.3rem 0 1.6rem; }
.lab-matrix > div > span {
  font: 700 .64rem var(--mono); letter-spacing: .07em; text-transform: uppercase; color: var(--ember);
}
.lab-matrix a { display: inline-block; margin-top: .65rem; font: 650 .78rem var(--sans); text-decoration: none; }

/* -------- lesson recipe ------------------------------------------------ */
.lesson-recipe {
  display: grid; grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1px; margin: 1.2rem 0 1.8rem; overflow: hidden;
  border: 1px solid var(--rule); border-radius: 11px; background: var(--rule);
}
.lesson-recipe > div {
  position: relative; min-height: 5.2rem; padding: .78rem .9rem .82rem 1rem;
  background: var(--panel);
}
.lesson-recipe > div::before {
  content: ""; position: absolute; left: 0; top: .78rem; bottom: .78rem;
  width: 2px; background: color-mix(in srgb, var(--link) 62%, transparent);
}
.lesson-recipe.advanced > div::before { background: color-mix(in srgb, var(--ember) 68%, transparent); }
.lesson-recipe span {
  display: block; margin-bottom: .25rem; color: var(--muted);
  font: 700 .61rem/1.3 var(--sans); letter-spacing: .09em; text-transform: uppercase;
}
.lesson-recipe strong {
  display: block; color: var(--ink); font-size: .89rem; line-height: 1.48;
}

.taste-check {
  position: relative; margin: 1.2rem 0 1.7rem; padding: .9rem 1rem .8rem 1.15rem;
  border: 1px solid color-mix(in srgb, var(--link) 28%, var(--rule));
  border-left: 3px solid var(--link); border-radius: 9px;
  background: color-mix(in srgb, var(--link) 5%, var(--panel));
}
.taste-check.advanced {
  border-color: color-mix(in srgb, var(--ember) 30%, var(--rule));
  border-left-color: var(--ember);
  background: color-mix(in srgb, var(--ember-bg) 48%, var(--panel));
}
.taste-check > strong {
  display: block; margin-bottom: .5rem; font: 700 .84rem/1.45 var(--sans);
}
.taste-check ol { margin: 0; padding-left: 1.25rem; }
.taste-check li { margin-bottom: .32rem; color: var(--ink-soft); font-size: .88rem; line-height: 1.55; }
.taste-check li:last-child { margin-bottom: 0; }

/* links get a quiet underline; nav-like links elsewhere don't */
.prose a { text-decoration: underline; text-decoration-color: color-mix(in srgb, var(--link) 40%, transparent); }
.prose a:hover { text-decoration-color: currentColor; }

/* -------- figures ------------------------------------------------------ */
.prose img { max-width: 100%; height: auto; display: block; }
.prose p > img { margin: 1.5rem 0; }
.prose figure { margin: 1.6rem 0; }
.prose figcaption { font-size: .82rem; color: var(--muted); margin-top: .5rem; }

/* -------- tables ------------------------------------------------------- */
.table-wrap { overflow-x: auto; margin: 1.3rem 0; }
.prose table {
  border-collapse: collapse; width: 100%; font-size: .89rem;
  font-variant-numeric: tabular-nums;
}
.prose th {
  text-align: left; font-family: var(--sans); font-size: .72rem; font-weight: 650;
  letter-spacing: .06em; text-transform: uppercase; color: var(--muted);
  padding: .45rem .7rem; border-bottom: 1.5px solid var(--rule); white-space: nowrap;
}
.prose td { padding: .48rem .7rem; border-bottom: 1px solid var(--rule-soft); vertical-align: top; }
.prose tbody tr:last-child td { border-bottom: none; }
.prose tbody tr:hover { background: var(--rule-soft); }

/* -------- code --------------------------------------------------------- */
.prose code {
  font-family: var(--mono); font-size: .855em;
  background: var(--code-bg); padding: .12em .34em; border-radius: 4px;
  overflow-wrap: break-word;
}
.prose pre {
  background: var(--code-bg); border: 1px solid var(--rule-soft);
  border-radius: 9px; padding: .95rem 1.05rem; overflow-x: auto;
  margin: 1.25rem 0; font-size: .83rem; line-height: 1.62;
  scrollbar-width: thin;
}
.prose pre code { background: none; padding: 0; font-size: inherit; }
.code-wrap { position: relative; }
.copy-btn {
  position: absolute; top: .5rem; right: .5rem;
  font-family: var(--sans); font-size: .7rem; letter-spacing: .03em;
  padding: .22rem .5rem; border-radius: 5px; cursor: pointer;
  background: var(--panel); color: var(--muted);
  border: 1px solid var(--rule); opacity: 0; transition: opacity .13s;
}
.code-wrap:hover .copy-btn, .copy-btn:focus-visible { opacity: 1; }
.copy-btn.done { color: var(--ember); border-color: var(--ember); }

/* pygments */
.hl .c, .hl .c1, .hl .cm, .hl .cs { color: var(--faint); font-style: italic; }
.hl .k, .hl .kn, .hl .kd, .hl .kc, .hl .kr, .hl .ow { color: var(--ember); }
.hl .s, .hl .s1, .hl .s2, .hl .sd, .hl .sb, .hl .se { color: #7fb98f; }
.hl .mi, .hl .mf, .hl .mh, .hl .il { color: #b39ae0; }
:root[data-theme="light"] .hl .s, :root[data-theme="light"] .hl .s1, :root[data-theme="light"] .hl .s2,
:root[data-theme="light"] .hl .sd, :root[data-theme="light"] .hl .sb, :root[data-theme="light"] .hl .se { color: #3f7d54; }
:root[data-theme="light"] .hl .mi, :root[data-theme="light"] .hl .mf, :root[data-theme="light"] .hl .mh, :root[data-theme="light"] .hl .il { color: #7a5cb0; }
.hl .nf, .hl .fm { color: var(--link); }
.hl .nc, .hl .nn { color: var(--link); font-weight: 600; }
.hl .nb, .hl .bp { color: var(--ink-soft); }
.hl .nd { color: var(--ember); }
.hl .o, .hl .p { color: var(--muted); }
:root[data-theme="dark"] .hl .s, :root[data-theme="dark"] .hl .s1,
:root[data-theme="dark"] .hl .s2, :root[data-theme="dark"] .hl .sd { color: #7fb98f; }
:root[data-theme="dark"] .hl .mi, :root[data-theme="dark"] .hl .mf,
:root[data-theme="dark"] .hl .mh { color: #b39ae0; }

/* -------- math --------------------------------------------------------- */
.katex { font-size: 1.03em; }
.katex-display {
  overflow-x: auto; overflow-y: hidden;
  padding: .55rem 0; margin: 1.15rem 0;
}
.katex-display > .katex { text-align: left; }

/* -------- progressive depth ---------------------------------------------
   The main line of a note stays a five-minute read; derivations and edge
   cases live in <details>, which GitHub renders too, so the layering is not
   a site-only feature. */
.prose details {
  margin: 1.4rem 0; border: 1px solid var(--rule); border-radius: 9px;
  background: var(--panel); overflow: hidden;
}
.prose details > summary {
  display: flex; align-items: center; gap: .5rem;
  padding: .6rem .9rem; cursor: pointer; list-style: none;
  font-family: var(--sans); font-size: .84rem; color: var(--ink-soft);
}
.prose details > summary::-webkit-details-marker,
.prose details > summary::marker { display: none; content: ""; }
.prose details > summary:hover { background: var(--rule-soft); color: var(--ink); }
.prose details > summary b {
  font-size: .62rem; font-weight: 700; letter-spacing: .1em; text-transform: uppercase;
  color: var(--ember); border: 1px solid color-mix(in srgb, var(--ember) 45%, transparent);
  border-radius: 4px; padding: .1rem .34rem; flex: none;
}
.prose details > summary::after {
  content: ""; flex: none; margin-left: auto; width: 7px; height: 7px;
  border-right: 1.7px solid var(--faint); border-bottom: 1.7px solid var(--faint);
  transform: rotate(45deg) translate(-2px, -2px); transition: transform .16s ease;
}
.prose details[open] > summary::after { transform: rotate(-135deg); }
.prose details[open] > summary { border-bottom: 1px solid var(--rule-soft); }
.prose details > *:not(summary) { margin-left: .9rem; margin-right: .9rem; }
.prose details > *:nth-child(2) { margin-top: .85rem; }
.prose details > *:last-child { margin-bottom: .85rem; }
.prose details .katex-display { margin: .9rem 0; }

/* -------- glossary terms ----------------------------------------------- */
.term {
  border-bottom: 1px dotted color-mix(in srgb, var(--ember) 60%, transparent);
  cursor: help; position: relative;
}
.term-en {
  font-family: var(--sans); font-size: .74em; color: var(--muted);
  margin: 0 .08em; overflow-wrap: anywhere;
}
.term::after {
  content: attr(data-tip);
  position: absolute; right: 0; top: calc(100% + 7px); z-index: 20;
  min-width: 12rem; max-width: 20rem; width: max-content;
  font-family: var(--sans); font-size: .76rem; line-height: 1.5; font-style: normal;
  color: var(--ink); background: var(--panel);
  border: 1px solid var(--rule); border-radius: 7px;
  padding: .45rem .6rem; box-shadow: var(--shadow);
  opacity: 0; visibility: hidden; transform: translateY(-3px);
  transition: opacity .14s, transform .14s, visibility .14s;
  pointer-events: none;
}
.term:hover::after, .term:focus::after { opacity: 1; visibility: visible; transform: translateY(0); }

.page-glossary {
  margin-top: 2.5rem; padding-top: 1.15rem; border-top: 1px solid var(--rule-soft);
  font-family: var(--sans);
}
.page-glossary details { border: 1px solid var(--rule); border-radius: 9px; background: var(--panel); }
.page-glossary summary {
  cursor: pointer; list-style: none; padding: .68rem .85rem;
  color: var(--ink-soft); font-size: .84rem; font-weight: 650;
}
.page-glossary summary::-webkit-details-marker { display: none; }
.page-glossary summary::after { content: "+"; float: right; color: var(--muted); }
.page-glossary details[open] summary::after { content: "−"; }
.page-glossary summary > span {
  margin-left: .35rem; padding: .06rem .34rem; border-radius: 999px;
  background: var(--ember-bg); color: var(--ember); font-size: .68rem;
}
.page-glossary dl { margin: 0; padding: .15rem .85rem .75rem; }
.page-glossary .gloss-row {
  display: grid; grid-template-columns: minmax(9rem, .7fr) 1.3fr; gap: 1rem;
  padding: .58rem 0; border-top: 1px solid var(--rule-soft);
}
.page-glossary dt { color: var(--ink); font-size: .82rem; font-weight: 600; }
.page-glossary dt span { color: var(--muted); font-size: .76rem; font-weight: 450; }
.page-glossary dd { margin: 0; color: var(--ink-soft); font-size: .78rem; line-height: 1.55; }

/* -------- live widget --------------------------------------------------- */
.widget {
  margin: 1.7rem 0; border: 1px solid var(--rule); border-radius: 11px;
  background: var(--panel); overflow: hidden;
}
.widget-head {
  display: flex; align-items: center; gap: .55rem;
  padding: .6rem .9rem; border-bottom: 1px solid var(--rule-soft);
  background: color-mix(in srgb, var(--ember-bg) 60%, transparent);
}
.widget-kicker {
  font-family: var(--sans); font-size: .62rem; font-weight: 700; letter-spacing: .1em;
  text-transform: uppercase; color: var(--ember);
  border: 1px solid color-mix(in srgb, var(--ember) 45%, transparent);
  border-radius: 4px; padding: .1rem .32rem;
}
.widget-title { font-size: .87rem; font-weight: 600; }
.widget-body { padding: .9rem; }
.xor-canvas { width: 100%; height: auto; display: block; border-radius: 7px; }
.widget-controls {
  display: flex; flex-wrap: wrap; align-items: center; gap: .5rem .95rem;
  margin-top: .8rem; font-family: var(--sans); font-size: .8rem;
}
.switch, .slider { display: flex; align-items: center; gap: .4rem; cursor: pointer; }
.slider input[type="range"] { width: 92px; accent-color: var(--ember); }
.switch input { accent-color: var(--ember); width: 15px; height: 15px; }
.slider output { font-family: var(--mono); font-size: .78rem; color: var(--muted); min-width: 1.2rem; }
.btn {
  font: inherit; font-size: .78rem; padding: .28rem .62rem; cursor: pointer;
  background: var(--paper); color: var(--ink-soft);
  border: 1px solid var(--rule); border-radius: 6px;
}
.btn:hover { border-color: var(--ember); color: var(--ember); }
.xor-stats { margin-left: auto; display: flex; gap: .9rem; }
.xor-stats .stat { display: flex; flex-direction: column; line-height: 1.15; }
.xor-stats b { font-family: var(--mono); font-size: .84rem; font-variant-numeric: tabular-nums; }
.xor-stats i { font-style: normal; font-size: .64rem; color: var(--muted); letter-spacing: .04em; }

/* -------- footer -------------------------------------------------------- */
.page-foot { max-width: 45rem; margin-top: 3.5rem; padding-top: 1.3rem; border-top: 1px solid var(--rule); }
.foot-meta { font-family: var(--sans); font-size: .8rem; color: var(--muted); display: flex; flex-wrap: wrap; gap: .45rem; }
.foot-meta a { color: var(--muted); text-decoration: none; }
.foot-meta a:hover { color: var(--ember); }
.foot-meta .sep { color: var(--rule); }
/* Page feedback: a prefilled GitHub issue, confirmed by the reader on GitHub. */
.page-feedback {
  margin: 0 0 1.4rem; padding: 1.15rem 1.2rem 1rem; font-family: var(--sans);
  border-radius: 16px 3px 16px 3px; background: color-mix(in srgb, var(--panel) 55%, transparent);
}
.pf-heading { margin: 0 0 .75rem; font: 650 .92rem/1.4 var(--sans); color: var(--ink); }
.pf-kinds { display: flex; flex-wrap: wrap; gap: .5rem; }
.pf-kind {
  display: inline-flex; align-items: center; min-height: 2.25rem; padding: 0 .95rem;
  border: 1px solid var(--rule); border-radius: 999px; color: var(--ink-soft);
  font-size: .82rem; text-decoration: none; cursor: pointer;
  transition: border-color .15s ease, background .15s ease, color .15s ease;
}
.pf-kind:hover { border-color: color-mix(in srgb, var(--ember) 55%, var(--rule)); color: var(--ink); }
.pf-kind[aria-pressed="true"] { border-color: var(--ember); background: var(--ember-bg); color: var(--ember); }
.pf-form { display: grid; gap: .55rem; margin-top: .9rem; }
.pf-form[hidden], .pf-quote[hidden], .pf-tip[hidden], .pf-thanks[hidden] { display: none; }
.pf-label { font-size: .78rem; color: var(--muted); }
.pf-text {
  box-sizing: border-box; width: 100%; min-height: 6.5rem; resize: vertical; padding: .7rem .8rem;
  border: 1px solid var(--rule); border-radius: 10px; background: var(--paper); color: var(--ink);
  font: .9rem/1.6 var(--sans);
}
.pf-text::placeholder { color: var(--faint); }
.pf-text:focus { outline: none; border-color: var(--ember); box-shadow: 0 0 0 3px var(--ember-bg); }
.pf-quote {
  display: flex; align-items: flex-start; gap: .55rem; margin: 0; padding: .55rem .7rem;
  border-left: 2px solid var(--ember); border-radius: 0 8px 8px 0; background: var(--ember-bg);
  font-size: .8rem; line-height: 1.6; color: var(--ink-soft);
}
.pf-quote q { flex: 1; quotes: none; overflow-wrap: anywhere; }
.pf-quote-label { color: var(--muted); white-space: nowrap; }
.pf-unquote { padding: 0 .2rem; border: 0; background: none; color: var(--muted); font-size: 1rem; line-height: 1.4; cursor: pointer; }
.pf-tip, .pf-note { margin: 0; font-size: .74rem; line-height: 1.6; color: var(--muted); }
.pf-actions { display: flex; flex-wrap: wrap; align-items: center; gap: .6rem; }
.pf-submit {
  min-height: 2.3rem; padding: 0 1.05rem; border: 0; border-radius: 999px;
  background: var(--ember); color: var(--paper); font: 650 .82rem/1 var(--sans); cursor: pointer;
}
.pf-submit:hover { filter: brightness(1.07); }
.pf-cancel { min-height: 2.3rem; padding: 0 .7rem; border: 0; background: none; color: var(--muted); font: .82rem/1 var(--sans); cursor: pointer; }
.pf-cancel:hover { color: var(--ink); }
.pf-count { margin-left: auto; font-size: .74rem; color: var(--muted); font-variant-numeric: tabular-nums; }
.pf-thanks { margin: .85rem 0 0; font-size: .82rem; color: var(--ember); }
.pf-more {
  display: flex; flex-wrap: wrap; gap: .4rem 1.15rem; margin-top: 1rem; padding-top: .8rem;
  border-top: 1px solid var(--rule-soft); font-size: .8rem;
}
.pf-more a { color: var(--ember); text-decoration: none; }
.pf-more a:hover { text-decoration: underline; text-underline-offset: 3px; }
.pf-review { margin: .55rem 0 0; font-size: .74rem; line-height: 1.7; color: var(--muted); overflow-wrap: anywhere; }
.pf-review a { color: var(--muted); }
.page-feedback a:focus-visible, .page-feedback button:focus-visible { outline: 2px solid var(--ember); outline-offset: 3px; }
@media print { .page-feedback { display: none; } }
.collab-table { overflow-x: auto; }
.collab-table td { overflow-wrap: anywhere; }

/* ---------------------------------------------------------------- responsive */
@media (min-width: 1081px) {
  .topbar {
    position: fixed; top: 0; right: 0; left: auto; width: auto;
    height: 52px; background: none; backdrop-filter: none; border: none; padding-right: 1.2rem;
  }
  .topbar .menu, .topbar-brand { display: none; }
  .side-scrim { display: none !important; }
}

@media (max-width: 1080px) {
  .shell { grid-template-columns: minmax(0, 1fr); padding: 0 1.15rem; }
  .rail { display: none; }
  .side {
    position: fixed; z-index: 50; top: 52px; left: 0;
    width: min(86vw, 320px); height: calc(100dvh - 52px);
    background: var(--panel); border-right: 1px solid var(--rule);
    padding: 1.3rem 1rem 3rem; box-shadow: var(--shadow);
    transform: translateX(-102%); transition: transform .22s ease;
  }
  .side.open { transform: none; }
  .side-scrim { position: fixed; inset: 52px 0 0; z-index: 45; background: rgba(10,12,15,.4); }
  main { padding-top: 1.5rem; }
  .prose h1 { font-size: 1.7rem; }
}

@media (max-width: 620px) {
  body { font-size: 16.5px; }
  .prose h1 { font-size: 1.5rem; }
  .prose h2 { font-size: 1.2rem; }
  .xor-stats { margin-left: 0; width: 100%; }
  .term::after {
    position: fixed; left: 1rem; right: 1rem; top: auto; bottom: 1rem;
    width: auto; min-width: 0; max-width: none;
  }
  .page-glossary .gloss-row { grid-template-columns: 1fr; gap: .18rem; }
  .curriculum-hero, .curriculum-grid, .lab-matrix, .lesson-recipe { grid-template-columns: 1fr; }
  .curriculum-grid .curriculum-card:last-child:nth-child(odd) { grid-column: auto; }
  .learning-path { grid-template-columns: 1fr; gap: 0; margin-left: .15rem; }
  .learning-path::before { top: 1rem; bottom: 1rem; left: 1rem; right: auto; border-top: 0; border-left: 1px solid var(--rule); }
  .learning-path a { display: grid; grid-template-columns: 2.1rem 1fr; grid-template-rows: auto auto; column-gap: .75rem; text-align: left; align-items: center; padding: .35rem 0; }
  .learning-path span { grid-row: 1 / 3; }
  .learning-path strong, .learning-path small { margin: 0; }
}

/* --- the rest of the editorial system ----------------------------------- */
.side {
  padding-top: 2rem; border-right: 0;
  mask-image: linear-gradient(to bottom, transparent 0, #000 1.1rem, #000 calc(100% - 2.5rem), transparent);
}
.brand { padding: 0 .55rem; }
.brand-mark {
  display: grid; place-items: center; width: 2.35rem; height: 2.35rem;
  border-radius: 50%; background: var(--panel); box-shadow: var(--shadow);
}
.brand-text b { font-size: 1.12rem; }
.brand-text i { max-width: 12rem; }
.search { margin: 1.45rem .45rem .65rem; }
.side-nav { margin-top: 1.3rem; }
.nav .grp + .grp { margin-top: .45rem; }
.nav details > summary {
  padding: .5rem .65rem; letter-spacing: .035em; text-transform: none;
  font-size: .76rem; border-radius: 10px;
}
.grp-count { padding: .08rem .35rem; border-radius: 999px; background: var(--rule-soft); }
.grp-body { padding: .5rem 0 .7rem .4rem; }
.nav .sec { margin-bottom: 1rem; }
.sec-name { letter-spacing: .025em; font-size: .7rem; }
.nav .sec > ul > li > a {
  margin: .12rem 0; padding: .32rem .65rem .32rem .85rem;
  border-left: 0; border-radius: 9px 3px 3px 9px; font-size: .86rem;
}
.nav .sec > ul > li > a.active {
  color: var(--ink); background: color-mix(in srgb, var(--ember-bg) 78%, var(--panel));
  box-shadow: inset 3px 0 var(--ember);
}
.side-foot { margin: 1.5rem .55rem 0; }

.rail { padding-top: 3.5rem; }
.rail-inner {
  position: relative; padding: 1rem 1rem 1.05rem 1.05rem;
  border-radius: 16px 4px 16px 4px;
  background: color-mix(in srgb, var(--panel) 54%, transparent);
}
.rail-inner::before {
  content: ""; position: absolute; left: 0; top: 1rem; width: 3px; height: 2.4rem;
  background: var(--moss); border-radius: 0 3px 3px 0;
}
.rail-title { letter-spacing: .08em; color: var(--moss); }
.toc ul { border-left-color: color-mix(in srgb, var(--rule) 72%, transparent); }
.toc li a { padding-top: .28rem; padding-bottom: .28rem; }
.toc li a.active { color: var(--ink); border-left-color: var(--ember); font-weight: 650; }

.chapter-mark {
  position: absolute; right: 0; top: -.7rem; z-index: -1;
  font: normal 8.5rem/.8 var(--serif); letter-spacing: -.08em;
  color: color-mix(in srgb, var(--ember) 7%, transparent); user-select: none;
}

.mobile-toc { display: none; }

.page-home .prose,
.page-home .page-foot,
.page-index .prose,
.page-index .page-foot { max-width: 55rem; }
.page-home .article-head {
  min-height: 25rem; display: flex; flex-direction: column; justify-content: flex-end;
  padding: 4rem 1.5rem 3.2rem; margin-bottom: 2.7rem;
  border-radius: 4px 36px 4px 36px;
  background:
    linear-gradient(135deg, color-mix(in srgb, var(--panel) 92%, transparent), color-mix(in srgb, var(--ember-bg) 38%, transparent));
  box-shadow: var(--shadow);
  overflow: hidden;
}
.page-home .article-head::before {
  inset: auto 1.5rem 1.35rem; width: auto; height: 2px;
  background: linear-gradient(90deg, var(--ember), #db9a4f 28%, var(--link) 58%, transparent 88%);
}
.page-home .article-head::after {
  content: "∿"; position: absolute; right: 1.7rem; top: .8rem;
  font: 11rem/.8 var(--serif); color: color-mix(in srgb, var(--link) 7%, transparent);
  transform: rotate(-12deg); pointer-events: none;
}
.page-home .article-head h1 { max-width: 10ch; font-size: clamp(4rem, 8vw, 6.8rem); }
.page-home .article-meta { max-width: 30rem; }
.page-index .article-head {
  margin-bottom: 2.7rem; padding-top: 2rem; padding-bottom: 2.7rem;
  border-bottom: 1px dashed color-mix(in srgb, var(--rule) 72%, transparent);
}
.page-index .article-head h1 { max-width: 19ch; }
.page-index .article-body > p:first-of-type { max-width: 48rem; }
.page-workshop .article-head::before { background: linear-gradient(var(--moss), transparent); }
.page-workshop .article-kicker span { color: var(--moss); }
.page-workshop .article-body pre {
  background: #201f1b; color: #f1eadf; border-color: #302d27;
  box-shadow: 0 22px 60px -38px rgba(0,0,0,.8);
}
.page-guide .article-head h1 { max-width: 18ch; }
.page-guide .article-body details.interview {
  border: 0; border-left: 3px solid var(--ember);
  background: color-mix(in srgb, var(--panel) 76%, transparent);
}

.curriculum-hero > div, .lab-matrix > div, .curriculum-card {
  border: 0; border-radius: 4px 18px 4px 18px;
  background: color-mix(in srgb, var(--panel) 78%, transparent);
  box-shadow: var(--shadow);
}
.curriculum-card { min-height: 12rem; padding: 1.25rem 1.35rem; }
.curriculum-card:hover {
  transform: translateY(-4px) rotate(-.15deg);
  border-color: transparent; box-shadow: 0 24px 52px -36px rgba(61,47,30,.6);
}
.lesson-recipe {
  gap: .65rem; padding: .65rem; border: 0; border-radius: 18px 4px 18px 4px;
  background: color-mix(in srgb, var(--panel) 52%, transparent); box-shadow: var(--shadow);
}
.lesson-recipe > div { border-radius: 10px 2px 10px 2px; }
.taste-check { border: 0; border-left: 3px solid var(--link); border-radius: 2px 15px 15px 2px; box-shadow: var(--shadow); }
.widget { border: 0; border-radius: 5px 18px 5px 18px; box-shadow: var(--shadow); }
.widget-head { padding: .8rem 1rem; }

.page-glossary { border-top-style: dashed; }
.page-glossary details { border: 0; border-radius: 14px 3px 14px 3px; box-shadow: var(--shadow); }

.page-turn {
  display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 1rem;
  max-width: 48rem; margin: 5rem 0 1rem; padding-top: 1.4rem;
  border-top: 1px dashed var(--rule);
}
.page-turn a {
  min-height: 7rem; display: flex; flex-direction: column; justify-content: space-between;
  padding: 1rem 1.1rem; color: var(--ink); text-decoration: none;
  border-radius: 3px 15px 3px 15px;
  background: color-mix(in srgb, var(--panel) 68%, transparent); box-shadow: var(--shadow);
  transition: transform .16s ease, background .16s ease;
}
.page-turn a:hover { transform: translateY(-3px); background: var(--panel); }
.page-turn small { font: .72rem/1.2 var(--sans); color: var(--ember); }
.page-turn strong { max-width: 24ch; font-size: .95rem; line-height: 1.45; }
.page-turn-next { text-align: right; align-items: flex-end; }

.page-foot {
  margin-top: 2.8rem; padding: 1.3rem 0 5rem; border-top: 0;
}
.foot-meta { padding: .8rem 0; border-top: 1px solid var(--rule-soft); border-bottom: 1px solid var(--rule-soft); }
.contrib { padding: 1.1rem 1.2rem; border-radius: 16px 3px 16px 3px; background: color-mix(in srgb, var(--panel) 45%, transparent); }

@media (max-width: 1080px) {
  .side { mask-image: none; }
  .mobile-toc {
    display: block; margin: -1.7rem 0 2.4rem; border: 0; border-radius: 13px;
    background: color-mix(in srgb, var(--panel) 68%, transparent); box-shadow: var(--shadow);
  }
  .mobile-toc summary {
    padding: .8rem 1rem; list-style: none; cursor: pointer;
    font: 650 .8rem/1.3 var(--sans); color: var(--ink-soft);
  }
  .mobile-toc summary::-webkit-details-marker { display: none; }
  .mobile-toc summary span { float: right; color: var(--faint); }
  .mobile-toc nav { padding: 0 1rem 1rem; }
  .mobile-toc ul { list-style: none; padding: 0; columns: 2; column-gap: 1rem; }
  .mobile-toc li { break-inside: avoid; margin: 0; }
  .mobile-toc a { display: block; padding: .24rem 0; font: .78rem/1.4 var(--sans); text-decoration: none; }
  .mobile-toc .l3 { padding-left: .65rem; }
}
@media (max-width: 620px) {
  .page-home .article-head { min-height: 21rem; padding: 2.3rem 1.1rem 2.6rem; border-radius: 3px 24px 3px 24px; }
  .page-home .article-head h1 { font-size: clamp(3.3rem, 18vw, 5rem); }
  .mobile-toc ul { columns: 1; }
  .page-turn { grid-template-columns: 1fr; margin-top: 3.8rem; }
  .page-turn-empty { display: none; }
  .page-turn a { min-height: 5.7rem; }
}

/* -------- foldable blocks inside prose ---------------------------------- */
.prose details {
  margin: 1.2rem 0; border: 1px solid var(--rule); border-radius: 9px;
  background: var(--panel); overflow: hidden;
}
.prose details > summary {
  padding: .58rem .85rem; cursor: pointer; list-style: none;
  font-family: var(--sans); font-size: .85rem; line-height: 1.45;
  display: flex; align-items: center; gap: .55rem;
}
.prose details > summary::-webkit-details-marker,
.prose details > summary::marker { display: none; content: ""; }
.prose details > summary::after {
  content: ""; flex: none; margin-left: auto; width: 6px; height: 6px;
  border-right: 1.6px solid var(--muted); border-bottom: 1.6px solid var(--muted);
  transform: rotate(45deg); transition: transform .16s ease;
}
.prose details[open] > summary::after { transform: rotate(-135deg); }
.prose details > summary:hover { background: var(--rule-soft); }
.prose details[open] > summary { border-bottom: 1px solid var(--rule-soft); }
.prose details > *:not(summary) { padding-left: .85rem; padding-right: .85rem; }
.prose details > *:last-child { padding-bottom: .5rem; }
.prose details > .code-wrap { padding: 0 .6rem; }

/* a runnable implementation */
.prose details.code-drop > summary { color: var(--link); }
.prose details.code-drop > summary b { color: var(--ink); }

/* an interview question: the summary IS the question */
.prose details.interview { border-left: 3px solid var(--ember); }
.prose details.interview > summary { font-weight: 600; }
.prose details.interview > summary::before {
  content: "Q"; flex: none;
  font-family: var(--mono); font-size: .68rem; font-weight: 700;
  color: var(--ember); border: 1px solid color-mix(in srgb, var(--ember) 45%, transparent);
  border-radius: 4px; padding: .04rem .3rem;
}
.prose details.interview + details.interview { margin-top: -.6rem; }

/* ========================================================================== */
/* 2026 editorial redesign — warm field notes, not a documentation dashboard  */
/* ========================================================================== */


body {
  background:
    radial-gradient(circle at 72% -10%, color-mix(in srgb, var(--ember) 7%, transparent), transparent 28rem),
    radial-gradient(circle at 5% 35%, color-mix(in srgb, var(--link) 5%, transparent), transparent 30rem),
    var(--paper);
}

.reading-progress {
  position: fixed; z-index: 100; inset: 0 0 auto; height: 3px;
  pointer-events: none;
}
.reading-progress span {
  display: block; height: 100%; transform: scaleX(0); transform-origin: left;
  background: linear-gradient(90deg, var(--ember), #dc9b4f, var(--link));
  transition: transform .08s linear;
}

.shell { max-width: 1480px; gap: 0 3.4rem; }
main { padding-top: 2.8rem; }
.prose, .page-foot { max-width: 48rem; }

.article-head {
  position: relative; margin: 0 0 3.8rem; padding: 1.1rem 0 2.2rem 1.35rem;
}
.article-head::before {
  content: ""; position: absolute; inset: 1.2rem auto 0 0; width: 3px;
  border-radius: 999px;
  background: linear-gradient(var(--ember), color-mix(in srgb, var(--ember) 8%, transparent));
}
.article-kicker { display: flex; align-items: center; gap: .65rem; margin-bottom: 1rem; }
.article-kicker span {
  font: 750 .68rem/1 var(--sans); letter-spacing: .13em; text-transform: uppercase;
  color: var(--ember);
}
.article-kicker i { font: normal .78rem/1.2 var(--sans); color: var(--muted); }
.article-kicker i::before { content: "/"; margin-right: .65rem; color: var(--faint); }
.article-head h1 {
  max-width: 15ch; margin: 0; font-size: clamp(2.35rem, 4.6vw, 4.25rem);
  line-height: 1.05; letter-spacing: -.045em; font-weight: 650; text-wrap: balance;
}
.article-meta {
  display: flex; flex-wrap: wrap; align-items: center; gap: .55rem;
  margin-top: 1.35rem; font: .76rem/1.4 var(--sans); color: var(--muted);
}
.article-meta b { width: 3px; height: 3px; border-radius: 50%; background: var(--faint); }
.article-meta .page-position { margin-left: auto; font-family: var(--mono); color: var(--faint); }

.article-body > p:first-of-type {
  max-width: 42rem; font-size: 1.17rem; line-height: 1.78; color: var(--ink-soft);
}
.article-body p { margin-bottom: 1.25rem; }
.article-body h2 {
  position: relative; margin: 4.4rem 0 1.15rem; padding: 0; border: 0;
  font-size: 1.55rem; line-height: 1.28; letter-spacing: -.025em;
}
.article-body h2::before {
  content: ""; display: block; width: 2.4rem; height: 2px; margin-bottom: .85rem;
  background: linear-gradient(90deg, var(--ember), transparent);
}
.article-body h3 { margin-top: 2.6rem; font-size: 1.13rem; color: var(--ink); }
.article-body blockquote {
  position: relative; margin: 2rem -.8rem; padding: 1.15rem 1.35rem 1.15rem 2.9rem;
  border: 0; border-radius: 2px 16px 16px 2px;
  background: color-mix(in srgb, var(--panel) 72%, transparent);
  box-shadow: var(--shadow);
}
.article-body blockquote::before {
  content: "“"; position: absolute; left: .9rem; top: .4rem;
  font: 2.5rem/1 var(--serif); color: var(--ember);
}
.article-body blockquote p:last-child { margin-bottom: 0; }

.article-body .table-wrap,
.article-body .code-wrap,
.article-body details,
.article-body .widget {
  box-shadow: var(--shadow);
}
.article-body .table-wrap {
  position: relative;
  margin: 1.8rem -.8rem; padding: .35rem .8rem .6rem;
  border: 1px solid color-mix(in srgb, var(--rule) 72%, transparent);
  border-radius: 14px; background: color-mix(in srgb, var(--panel) 82%, transparent);
}
.article-body details { border-radius: 14px; border-color: color-mix(in srgb, var(--rule) 78%, transparent); }
.article-body pre { border-radius: 13px; padding: 1.1rem 1.2rem; }
.article-body .katex-display {
  margin: 1.65rem -.4rem; padding: 1rem .4rem;
  background: color-mix(in srgb, var(--panel) 42%, transparent); border-radius: 10px;
}

.bilingual-note {
  position: relative; margin: 1.55rem 0 1.9rem; padding: 1rem 1.15rem 1rem 1.3rem;
  border-left: 3px solid var(--link); border-radius: 2px 14px 14px 2px;
  background: color-mix(in srgb, var(--panel) 70%, transparent);
  box-shadow: var(--shadow);
}
.bilingual-note > span {
  display: block; margin-bottom: .45rem;
  font: 750 .65rem/1.2 var(--sans); letter-spacing: .1em; text-transform: uppercase;
  color: var(--link);
}
.bilingual-note p { margin: 0; font-size: .94rem; line-height: 1.72; color: var(--ink-soft); }
.bilingual-note strong { color: var(--ink); }
.bilingual-intro { border-left-color: var(--ember); }
.bilingual-intro > span { color: var(--ember); }

.concept-card {
  position: relative; margin: 2rem -.8rem 2.5rem; overflow: clip;
  border: 1px solid color-mix(in srgb, var(--rule) 74%, transparent);
  border-radius: 5px 20px 5px 20px;
  background: color-mix(in srgb, var(--panel) 82%, transparent);
  box-shadow: var(--shadow);
}
.concept-card.has-flip { cursor: pointer; }
.concept-card.is-en {
  border-color: color-mix(in srgb, var(--link) 38%, var(--rule));
  background: color-mix(in srgb, var(--panel) 88%, var(--link) 4%);
}
.concept-face { padding: 1.35rem 1.45rem 1.5rem; }
.concept-face > h3:first-child {
  max-width: calc(100% - 7rem); margin: .05rem 0 1.5rem;
  font-size: 1.22rem; line-height: 1.32;
}
.concept-face > h2:first-child {
  max-width: calc(100% - 7rem); margin: .05rem 0 1.5rem; padding: 0;
  border: 0; font-size: 1.46rem; line-height: 1.28;
}
.concept-face > h2:first-child::before { display: none; }
.concept-title-en {
  max-width: calc(100% - 7rem); margin: .05rem 0 1.5rem;
  color: var(--ink); font: 650 1.22rem/1.32 var(--serif); letter-spacing: -.012em;
}
.concept-title-h2 { font-size: 1.46rem; line-height: 1.28; }
.concept-face > :last-child { margin-bottom: 0; }
.concept-face-en { font-family: var(--serif); }
.concept-flip {
  position: absolute; z-index: 4; top: 1rem; right: 1rem;
  display: inline-flex; align-items: center; gap: .45rem;
  min-height: 2rem; padding: .34rem .62rem .34rem .72rem;
  border: 1px solid color-mix(in srgb, var(--link) 30%, var(--rule));
  border-radius: 999px; background: var(--panel); color: var(--link);
  font: 700 .69rem/1 var(--sans); letter-spacing: .035em; cursor: pointer;
  box-shadow: 0 8px 22px -16px rgba(35, 74, 84, .65);
}
.concept-flip:hover { color: var(--link-hover); border-color: var(--link); }
.concept-flip:focus-visible { outline: 2px solid var(--link); outline-offset: 3px; }
.concept-flip i { font: normal .9rem/1 var(--sans); transition: transform .18s ease; }
.concept-card.is-en .concept-flip i { transform: rotate(180deg); }
.concept-card:not(.has-flip) .concept-face + .concept-face {
  border-top: 1px dashed var(--rule); background: color-mix(in srgb, var(--link) 4%, transparent);
}
.recipe-flip { cursor: pointer; }
.recipe-face { height: 100%; padding-right: 3.2rem; }
.recipe-flip.is-en { background: color-mix(in srgb, var(--panel) 90%, var(--link) 5%); }
.recipe-flip .concept-flip {
  top: .65rem; right: .65rem; min-height: 1.65rem;
  padding: .23rem .42rem .23rem .5rem; font-size: .58rem;
}
.lesson-recipe .recipe-flip .concept-flip span {
  display: inline; margin: 0; color: inherit; font: inherit; letter-spacing: inherit;
  text-transform: none;
}

@media (max-width: 620px) {
  .concept-card { margin-left: 0; margin-right: 0; border-radius: 4px 15px 4px 15px; }
  .concept-face { padding: 1.15rem 1rem 1.3rem; }
  .concept-face > h3:first-child { max-width: calc(100% - 5.8rem); font-size: 1.08rem; }
  .concept-face > h2:first-child { max-width: calc(100% - 5.8rem); font-size: 1.22rem; }
  .concept-title-en { max-width: calc(100% - 5.8rem); font-size: 1.08rem; }
  .concept-title-h2 { font-size: 1.22rem; }
  .concept-flip { top: .85rem; right: .8rem; }
}

@media (max-width: 1080px) {
  .shell { padding: 0 1.5rem; }
  main { padding-top: 2.1rem; }
  .article-head h1 { max-width: 18ch; }
}
@media (max-width: 620px) {
  .shell { padding: 0 1rem; }
  .article-head { margin-bottom: 2.8rem; padding-left: 1rem; }
  .article-head h1 { font-size: clamp(2rem, 11vw, 3rem); }
  .article-meta .page-position { margin-left: 0; }
  .article-body > p:first-of-type { font-size: 1.08rem; }
  .article-body h2 { margin-top: 3.5rem; font-size: 1.35rem; }
  .article-body blockquote, .article-body .table-wrap { margin-left: 0; margin-right: 0; }
}

/* ======================================================================
   Information architecture: category tabs, sidebar category headings,
   and the home page roadmap + category cards.
   ====================================================================== */

/* -------- top bar: the big directions ------------------------------------ */
.topbar-brand { display: flex; align-items: center; gap: .5rem; }
.topbar-brand svg { flex: 0 0 auto; color: var(--ember); }
.topbar-tabs {
  display: flex; align-items: stretch; gap: .15rem; min-width: 0; height: 100%;
  overflow-x: auto; scrollbar-width: none; font-family: var(--sans), var(--cjk);
}
.topbar-tabs::-webkit-scrollbar { display: none; }
.topbar-tabs a {
  position: relative; flex: 0 0 auto; display: flex; align-items: center; gap: .4rem; align-self: stretch;
  padding: 0 .85rem; text-decoration: none; white-space: nowrap;
  color: var(--muted); transition: color .15s ease;
}
.topbar-tabs .tab-sep { flex: 0 0 auto; align-self: center; width: 1px; height: 1rem; margin: 0 .35rem; background: var(--rule); }
.topbar-tabs a.tab-author span { font-weight: 600; }
.topbar-tabs a span { font-size: .9rem; font-weight: 650; letter-spacing: -.005em; }
.topbar-tabs a small { font-size: .68rem; font-weight: 500; color: var(--faint); transform: translateY(.06rem); }
.topbar-tabs a:hover { color: var(--ink); }
.topbar-tabs a.active { color: var(--ink); }
.topbar-tabs a::after {                   /* the chosen direction carries the ember underline */
  content: ""; position: absolute; left: .85rem; right: .85rem; bottom: 0; height: 3px; border-radius: 3px 3px 0 0;
  background: var(--ember); transform: scaleX(0); transition: transform .2s ease;
}
.topbar-tabs a:hover::after { transform: scaleX(.35); }
.topbar-tabs a.active::after { transform: scaleX(1); }
@media (min-width: 1081px) {
  /* A real header on desktop: brand above the sidebar, directions above the content column. */
  .topbar {
    position: sticky; top: 0; left: 0; right: auto; width: 100%; height: 52px;
    display: grid; grid-template-columns: var(--side-w) minmax(0, 1fr) auto; align-items: center; gap: 0 3.4rem;
    padding: 0 max(1.5rem, calc((100vw - 1480px) / 2 + 1.5rem));
    background: color-mix(in srgb, var(--paper) 88%, transparent); backdrop-filter: saturate(1.4) blur(10px);
    border-bottom: 1px solid var(--rule);
  }
  .topbar .menu { display: none; }
  .topbar-brand { display: flex; font-family: var(--body); font-size: 1.02rem; }
  .side .brand { display: none; }            /* the brand lives in the header now */
  .side { padding-top: 1.4rem; }
}
@media (max-width: 1080px) {
  .topbar-tabs a small { display: none; }
  .topbar-tabs a { padding: 0 .6rem; }
  .topbar-tabs a::after { left: .6rem; right: .6rem; }
}
.topbar-right { flex: 0 0 auto; }
.topbar-right .lang-btn { white-space: nowrap; }
@media (max-width: 620px) { .topbar-brand { display: none; } }

/* -------- second row: the blocks inside the chosen direction ---------------- */
.subtabs {
  display: flex; flex-wrap: wrap; align-items: center; gap: .35rem; margin: 0 0 1.6rem;
  font-family: var(--sans), var(--cjk);
}
.subtabs-label {
  margin-right: .35rem; font-size: .66rem; font-weight: 700; letter-spacing: .12em; text-transform: uppercase; color: var(--ember);
}
.subtabs a {
  display: inline-flex; align-items: baseline; gap: .35rem; padding: .36rem .75rem; border-radius: 999px;
  border: 1px solid var(--rule); background: var(--panel); text-decoration: none; white-space: nowrap;
  color: var(--ink-soft); transition: color .15s ease, border-color .15s ease, background .15s ease;
}
.subtabs a span { font-size: .8rem; font-weight: 600; }
.subtabs a small { font-size: .66rem; color: var(--faint); }
.subtabs a:hover { border-color: var(--ember); color: var(--ember); }
.subtabs a.active { background: var(--ink); border-color: var(--ink); color: var(--paper); }
.subtabs a.active small { color: color-mix(in srgb, var(--paper) 62%, transparent); }
@media (max-width: 760px) {
  .subtabs { flex-wrap: nowrap; overflow-x: auto; scrollbar-width: none; margin-bottom: 1.2rem; }
  .subtabs::-webkit-scrollbar { display: none; }
  .subtabs a small { display: none; }
}
@media print { .subtabs { display: none; } }

/* -------- sidebar category headings ------------------------------------- */
.nav .cat { list-style: none; margin: 1.15rem 0 .3rem; padding: 0 .55rem; }
.nav .cat:first-child { margin-top: .2rem; }
.nav .cat a, .nav .cat span {
  font-family: var(--sans), var(--cjk); font-size: .68rem; font-weight: 700; letter-spacing: .12em;
  text-transform: uppercase; color: var(--ember); text-decoration: none;
}
.nav .cat a:hover { text-decoration: underline; text-underline-offset: 3px; }

/* -------- home page blocks ---------------------------------------------- */
.home-block { margin: 2.6rem 0 0; font-family: var(--sans), var(--cjk); }
.block-head { display: grid; grid-template-columns: auto 1fr; align-items: baseline; gap: .1rem .8rem; }
.block-num { grid-row: span 2; font-family: var(--mono); font-size: 1.7rem; font-weight: 700; line-height: 1; color: var(--ember); }
.block-kicker { font-size: .66rem; font-weight: 700; letter-spacing: .14em; text-transform: uppercase; color: var(--muted); }
.article-body .block-title, .block-title {
  margin: 0; padding: 0; border: 0; font-family: var(--body); font-size: 1.55rem; line-height: 1.2; letter-spacing: -.015em;
}
.block-title::before, .block-title::after { content: none !important; }
.block-title em { margin-left: .6rem; font-family: var(--sans), var(--cjk); font-size: .8rem; letter-spacing: 0; }
.block-desc { grid-column: 2; margin: .35rem 0 0; max-width: 46rem; font-size: .9rem; line-height: 1.65; color: var(--ink-soft); }
.about-block { margin-bottom: 1.2rem; padding-bottom: 1.1rem; border-bottom: 1px solid var(--rule); }
.about-block + p { margin-top: 1.4rem; }

/* -------- roadmap -------------------------------------------------------- */
.roadmap {
  padding: 1.3rem 1.3rem 1.15rem; border-radius: 5px 22px 5px 22px;
  background: var(--panel); box-shadow: var(--shadow); font-family: var(--sans), var(--cjk);
}
.rm-tabs { display: flex; flex-wrap: wrap; gap: .3rem; margin-top: 1rem; }
.rm-tab.is-side { border-style: dashed; }
.rm-tab {
  font: inherit; font-size: .8rem; font-weight: 600; padding: .4rem .8rem; cursor: pointer;
  color: var(--ink-soft); background: var(--paper); border: 1px solid var(--rule); border-radius: 999px;
  transition: color .15s ease, border-color .15s ease, background .15s ease;
}
.rm-tab:hover { border-color: var(--ember); color: var(--ember); }
.rm-tab[aria-selected="true"] { background: var(--ink); border-color: var(--ink); color: var(--paper); }
.roadmap:not(.is-live) .rm-tabs { display: none; }            /* no JS: every track is simply listed */
.roadmap.is-live .rm-track:not(.is-current) { display: none; }
.rm-track { margin-top: 1.1rem; }
.roadmap:not(.is-live) .rm-track + .rm-track { margin-top: 2.2rem; padding-top: 1.4rem; border-top: 1px solid var(--rule); }
.rm-track-name { display: inline-block; margin-right: .6rem; font-family: var(--body); font-size: 1.28rem; letter-spacing: -.01em; }
.rm-blurb { margin: .35rem 0 0; max-width: 46rem; font-size: .88rem; line-height: 1.65; color: var(--ink-soft); }
.rm-kind {
  display: inline-block; vertical-align: .18em; padding: .14rem .5rem; border-radius: 999px; font-size: .66rem; font-weight: 700;
  color: var(--ember); background: var(--ember-bg);
}
.rm-kind.is-side { color: var(--muted); background: var(--code-bg); }
.rm-caveat {
  margin: .6rem 0 0; max-width: 46rem; padding: .55rem .75rem; border-left: 3px solid var(--faint); border-radius: 2px 8px 8px 2px;
  background: var(--code-bg); font-size: .8rem; line-height: 1.6; color: var(--ink-soft);
}
.rm-expand {
  margin-left: auto; font: inherit; font-size: .74rem; font-weight: 600; padding: .28rem .65rem; cursor: pointer;
  color: var(--ink-soft); background: none; border: 1px solid var(--rule); border-radius: 999px;
}
.rm-expand::before { content: attr(data-open); }
.rm-expand[aria-pressed="true"]::before { content: attr(data-close); }
.rm-expand:hover { border-color: var(--ember); color: var(--ember); }
.roadmap:not(.is-live) .rm-expand { display: none; }
.rm-progress { display: flex; align-items: center; gap: .7rem; margin-top: .8rem; }
.roadmap:not(.is-live) .rm-bar, .roadmap:not(.is-live) .rm-count { display: none; }
.rm-bar { flex: 1; max-width: 22rem; height: 6px; border-radius: 999px; background: var(--rule); overflow: hidden; }
.rm-bar i { display: block; height: 100%; width: 0; border-radius: inherit; background: linear-gradient(90deg, var(--ember), var(--link)); transition: width .4s ease; }
.rm-count { font-family: var(--mono); font-size: .74rem; color: var(--muted); font-variant-numeric: tabular-nums; }

/* the stack: role-specific layers on top, shared foundations at the bottom */
.stack-axis { margin: .9rem 0 .35rem; font-size: .68rem; font-weight: 600; letter-spacing: .06em; color: var(--faint); }
.stack + .stack-axis { margin: .45rem 0 0; }
.stack { display: grid; gap: .4rem; }
.stack-layer {
  border: 1px solid var(--rule); border-left: 4px solid var(--ember); border-radius: 4px 12px 12px 4px;
  background: var(--paper); overflow: hidden; transition: border-color .15s ease, box-shadow .15s ease;
}
.stack-layer.is-plus { border-left-color: var(--faint); }
.prose .stack-layer { margin: 0; box-shadow: none; border: 1px solid var(--rule); border-left: 4px solid var(--ember); border-radius: 4px 12px 12px 4px; }
.prose .stack-layer.is-plus { border-left-color: var(--faint); }
.prose .stack-layer[open] { box-shadow: var(--shadow); }
.prose .stack-layer > summary { border-bottom: 0; font-size: inherit; color: inherit; }
.prose .stack-layer > .sl-body { margin: 0; }
.prose .stack-layer .sl-body > * { margin-left: 0; margin-right: 0; }
.prose .stack-layer > summary {
  display: grid; grid-template-columns: 5rem minmax(0, 1fr) auto auto; align-items: center; gap: .3rem .9rem;
  padding: .7rem .9rem .7rem .8rem; cursor: pointer; list-style: none;
}
.stack-layer > summary::-webkit-details-marker { display: none; }
.prose .stack-layer > summary:hover { background: color-mix(in srgb, var(--ember-bg) 45%, transparent); }
.sl-weight { font-size: .66rem; font-weight: 700; letter-spacing: .05em; color: var(--ember); white-space: nowrap; }
.is-plus .sl-weight { color: var(--muted); }
.sl-name { display: flex; flex-wrap: wrap; align-items: baseline; gap: 0 .6rem; min-width: 0; }
.sl-name strong { font-size: .95rem; line-height: 1.35; letter-spacing: -.005em; }
.sl-name em, .rm-mod-alt, .block-title em, .cat-card strong em {
  font-style: normal; font-weight: 500; color: var(--muted);
}
.sl-name em { font-size: .74rem; }
.sl-tools { grid-column: 2; grid-row: 2; display: flex; flex-wrap: wrap; gap: .25rem; min-width: 0; }
.sl-weight, .sl-count, .prose .stack-layer > summary::after { grid-row: 1; }
.sl-count { grid-column: 3; }
.prose .stack-layer > summary::after { grid-column: 4; }
.sl-tools i {
  font-style: normal; font-family: var(--mono); font-size: .68rem; padding: .16rem .42rem; border-radius: 5px;
  color: var(--ink-soft); background: var(--code-bg); white-space: nowrap;
}
.sl-count { justify-self: end; font-family: var(--mono); font-size: .72rem; color: var(--muted); font-variant-numeric: tabular-nums; white-space: nowrap; }
.sl-body { padding: .1rem .9rem .9rem .8rem; border-top: 1px dashed var(--rule); }
.sl-shared { margin: .6rem 0 0; font-size: .74rem; color: var(--muted); }
.rm-modules { list-style: none; margin: .6rem 0 0; padding: 0; display: grid; grid-template-columns: repeat(auto-fill, minmax(15.5rem, 1fr)); gap: .45rem; }
.rm-mod {
  display: flex; align-items: stretch; min-width: 0; border: 1px solid var(--rule); border-radius: 9px;
  background: var(--paper); transition: border-color .15s ease, transform .15s ease, box-shadow .15s ease;
}
.rm-mod:not(.is-planned):hover { border-color: var(--link); transform: translateY(-1px); box-shadow: var(--shadow); }
.rm-mod a, .rm-planned { flex: 1; min-width: 0; display: flex; flex-direction: column; gap: .12rem; padding: .5rem .7rem .5rem .1rem; text-decoration: none; color: inherit; }
.rm-mod-title { font-size: .84rem; font-weight: 600; line-height: 1.4; color: var(--ink); }
.rm-mod a:hover .rm-mod-title { color: var(--link); }
.rm-mod-alt { font-size: .72rem; line-height: 1.35; }
.rm-mod-meta { font-size: .7rem; color: var(--muted); }
.rm-check, .rm-dot { flex: 0 0 auto; width: 2.1rem; display: grid; place-items: center; background: none; border: 0; padding: 0; }
.rm-check { cursor: pointer; }
.rm-check::before, .rm-dot::before {
  content: ""; width: .95rem; height: .95rem; border-radius: 50%; border: 1.6px solid var(--faint);
  transition: background .15s ease, border-color .15s ease;
}
.rm-check:hover::before { border-color: var(--link); }
.rm-check[aria-pressed="true"]::before {
  border-color: var(--link); background: var(--link)
    url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 12 12'%3E%3Cpath d='M2.6 6.3l2.2 2.2 4.6-4.9' fill='none' stroke='white' stroke-width='1.7' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E") center / 72% no-repeat;
}
.roadmap:not(.is-live) .rm-check { visibility: hidden; }
.rm-mod.is-done { background: color-mix(in srgb, var(--link) 7%, var(--paper)); }
.rm-mod.is-done .rm-mod-title { color: var(--ink-soft); }
.rm-mod.is-planned { border-style: dashed; background: none; }
.rm-mod.is-planned .rm-mod-title { font-weight: 500; color: var(--muted); }
.rm-dot::before { border-style: dashed; }
.rm-note { margin: .9rem 0 0; font-size: .76rem; line-height: 1.6; color: var(--muted); max-width: 48rem; }

/* -------- knowledge blocks, live figures, threads ------------------------- */
.rm-live, .viz-kicker i {
  font-style: normal; font-size: .58rem; font-weight: 700; letter-spacing: .1em; text-transform: uppercase; color: var(--ember);
  border: 1px solid color-mix(in srgb, var(--ember) 45%, transparent); border-radius: 4px; padding: .05rem .28rem; vertical-align: .12em;
}
.rm-live { margin-left: .3rem; }

.kb-area { display: grid; grid-template-columns: 7.5rem minmax(0, 1fr); gap: .6rem 1rem; margin-top: 1.15rem; align-items: start; }
.kb-area-name { position: sticky; top: 4.5rem; padding-top: .55rem; display: flex; flex-direction: column; }
.kb-area-name strong { font-family: var(--body); font-size: 1.05rem; }
.kb-area-name em, .kb-card em, .viz-card em, .thread-card em { font-style: normal; font-size: .72rem; font-weight: 500; color: var(--muted); }
.kb-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(13.5rem, 1fr)); gap: .5rem; }
.kb-card, .viz-card, .thread-card {
  display: flex; flex-direction: column; gap: .18rem; min-width: 0; padding: .7rem .8rem; text-decoration: none; color: inherit;
  border: 1px solid var(--rule); border-radius: 10px; background: var(--panel);
  transition: border-color .15s ease, transform .15s ease, box-shadow .15s ease;
}
a.kb-card:hover, a.viz-card:hover, a.thread-card:hover { border-color: var(--link); transform: translateY(-1px); box-shadow: var(--shadow); }
.kb-card strong, .viz-card strong, .thread-card strong { font-size: .88rem; line-height: 1.4; color: var(--ink); }
a.kb-card:hover strong, a.viz-card:hover strong, a.thread-card:hover strong { color: var(--link); }
.kb-meta, .kb-routes, .thread-meta { font-size: .7rem; color: var(--muted); }
.kb-meta { margin-top: .25rem; font-family: var(--mono); }
.kb-card.is-planned, .thread-card.is-planned { border-style: dashed; background: none; }
.kb-card.is-planned strong, .thread-card.is-planned strong { font-weight: 500; color: var(--muted); }

.viz-grid, .thread-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(16.5rem, 1fr)); gap: .55rem; margin-top: 1.15rem; }
.viz-kicker { display: flex; align-items: center; gap: .4rem; font-size: .68rem; color: var(--muted); }
.viz-desc, .thread-desc { margin-top: .2rem; font-size: .78rem; line-height: 1.55; color: var(--ink-soft); }
.thread-grid { grid-template-columns: repeat(auto-fill, minmax(19rem, 1fr)); }
.thread-card { border-left: 3px solid var(--link); border-radius: 3px 10px 10px 3px; }
.thread-card.is-planned { border-left-style: dashed; border-left-color: var(--faint); }
.thread-chips { display: flex; flex-wrap: wrap; gap: .25rem; margin-top: .45rem; }
.thread-chips i {
  font-style: normal; font-size: .66rem; padding: .12rem .4rem; border-radius: 999px; color: var(--ink-soft);
  background: var(--code-bg); white-space: nowrap;
}
.thread-meta { margin-top: .35rem; }
.article-body .kb-card, .article-body .viz-card, .article-body .thread-card { text-decoration: none; }
@media (max-width: 760px) {
  .kb-area { grid-template-columns: 1fr; }
  .kb-area-name { position: static; flex-direction: row; align-items: baseline; gap: .5rem; padding-top: 0; }
}

/* -------- quick-review question bank (interview/) ------------------------- */
.qb-tools {
  position: sticky; top: 3.6rem; z-index: 5; display: flex; flex-wrap: wrap; align-items: center; gap: .4rem;
  margin: 1.4rem 0 .4rem; padding: .5rem .7rem; border: 1px solid var(--rule); border-radius: 12px;
  background: color-mix(in srgb, var(--panel) 92%, transparent); backdrop-filter: blur(8px);
  font-family: var(--sans), var(--cjk);
}
.qb-count { margin-right: auto; font-size: .78rem; font-weight: 600; color: var(--muted); }
.q-meta, .q-sub { font-family: var(--sans), var(--cjk); font-size: .78rem; color: var(--muted); margin: .1rem 0 .6rem; }
.q-sub { margin-top: 1.1rem; font-weight: 700; letter-spacing: .02em; color: var(--ink-soft); }
.q-src { font-family: var(--sans), var(--cjk); font-size: .74rem; color: var(--muted); }
p.q-src { margin-top: .8rem; padding-top: .55rem; border-top: 1px dashed var(--rule); }
.prose details.qa { margin: .45rem 0; }
.prose details.qa > summary { font-weight: 600; }
.prose details.qa.is-picked { border-color: var(--ember); box-shadow: 0 0 0 2px var(--ember-bg), var(--shadow); }
.sl-questions { margin: .7rem 0 0; font-size: .78rem; font-weight: 600; }
.sl-questions a { text-decoration: none; }
.sl-questions a:hover { text-decoration: underline; text-underline-offset: 3px; }

/* -------- the three category cards --------------------------------------- */
.cat-cards { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: .8rem; margin: 1.2rem 0 0; font-family: var(--sans), var(--cjk); }
.cat-card {
  display: flex; flex-direction: column; gap: .3rem; padding: 1.05rem 1.1rem 1rem; text-decoration: none; color: inherit;
  border-radius: 18px 4px 18px 4px; background: var(--panel); box-shadow: var(--shadow);
  transition: transform .15s ease;
}
.cat-card:hover { transform: translateY(-2px); }
.cat-num { font-family: var(--mono); font-size: .7rem; font-weight: 700; color: var(--ember); }
.cat-card strong em { margin-left: .5rem; font-family: var(--sans), var(--cjk); font-size: .74rem; letter-spacing: 0; }
.cat-card strong { font-family: var(--body); font-size: 1.35rem; letter-spacing: -.01em; color: var(--ink); }
.cat-card:hover strong { color: var(--link); }
.cat-blurb { font-size: .84rem; line-height: 1.6; color: var(--ink-soft); }
.cat-meta { margin-top: .35rem; font-size: .72rem; color: var(--muted); }
.article-body .cat-card, .article-body .rm-mod a { text-decoration: none; }

@media (max-width: 760px) { .cat-cards { grid-template-columns: 1fr; } }
@media (max-width: 760px) {
  .prose .stack-layer > summary { grid-template-columns: minmax(0, 1fr) auto auto; }
  .sl-weight { grid-column: 1; grid-row: 1; } .sl-count { grid-column: 2; } .prose .stack-layer > summary::after { grid-column: 3; }
  .sl-name { grid-column: 1 / -1; grid-row: 2; } .sl-tools { grid-column: 1 / -1; grid-row: 3; }
}
@media (max-width: 620px) {
  .roadmap { padding: 1rem .85rem; }
  .rm-modules { grid-template-columns: 1fr; }
  .block-num { font-size: 1.35rem; }
  .block-title { font-size: 1.3rem; }
}

/* ======================================================================
   Night sky + hero (static/sky.js) and the black-and-white finish.
   ====================================================================== */
html { background: var(--paper); }
body { background: transparent; }
.sky { position: fixed; inset: 0; z-index: -1; width: 100%; height: 100%; display: block; background: #000; transition: opacity 1.1s ease; }
html.sky-back .sky { opacity: .12; }
:root[data-theme="light"] .sky { display: none; }
:root[data-theme="light"] body { background: var(--paper); }
.topbar { background: color-mix(in srgb, var(--paper) 78%, transparent); }
@media (min-width: 1081px) { .topbar { background: color-mix(in srgb, var(--paper) 78%, transparent); } }

.hero {
  position: relative; min-height: 100svh; display: flex; flex-direction: column; align-items: center; justify-content: center;
  text-align: center; padding: 4rem 1.5rem 26vh; font-family: var(--body);
}
.hero::before { content: ""; position: absolute; left: 50%; top: 50%; width: min(92vw, 980px); height: min(60vh, 420px); transform: translate(-50%, -56%);
  background: radial-gradient(ellipse at center, rgba(0,0,0,.62), rgba(0,0,0,.30) 45%, rgba(0,0,0,0) 72%); pointer-events: none; }
.hero-kicker { position: relative; font: 500 .78rem/1.5 var(--mono); letter-spacing: .18em; text-transform: uppercase; color: #CFCFCF; animation: hero-in 1.2s .1s ease both; }
.hero-title {
  max-width: 17ch; margin: 1.5rem 0 0; font-size: clamp(2.2rem, 5.6vw, 4.8rem); line-height: 1.05; letter-spacing: -.035em; font-weight: 500;
  position: relative; color: #FFFFFF; text-shadow: 0 2px 28px rgba(0,0,0,.7), 0 0 2px rgba(0,0,0,.6); text-wrap: balance; animation: hero-in 1.2s .25s ease both;
}
html.lang-zh .hero-title { font-weight: 600; letter-spacing: -.01em; }
.hero-scroll { position: absolute; left: 50%; bottom: 2.1rem; width: 22px; height: 36px; margin-left: -11px; border: 1.5px solid var(--rule); border-radius: 12px; animation: hero-in 1.2s .9s ease both; }
.hero-scroll span { position: absolute; left: 50%; top: 7px; width: 3px; height: 7px; margin-left: -1.5px; border-radius: 2px; background: var(--muted); animation: hero-wheel 2.2s 1.2s ease-in-out infinite; }
@keyframes hero-in { from { opacity: 0; transform: translateY(8px); } to { opacity: 1; transform: none; } }
@keyframes hero-wheel { 0%, 20% { transform: translateY(0); opacity: 1; } 70% { transform: translateY(12px); opacity: 0; } 71%, 100% { transform: translateY(0); opacity: 0; } }
.page-home .article-head { display: none; }        /* the hero is the home page's opening */
@media (prefers-reduced-motion: reduce) { .hero-kicker, .hero-title, .hero-scroll, .hero-scroll span { animation: none; } }
@media print { .hero, .sky { display: none; } }

/* the finish: one radius, hairlines instead of shadows; colour is set in the dawn block below */
.lesson-recipe, .lesson-recipe > div, .taste-check, .widget, .page-glossary details, .rail-inner, .article-body .table-wrap,
.article-body details, .article-body pre, .roadmap, .cat-card, .kb-card, .viz-card, .thread-card, .stack-layer, .rm-mod,
.qb-tools, .ro, .calc, .seg, .concept-card, .mobile-toc, .page-turn a { border-radius: 8px !important; box-shadow: none !important; }
.lesson-recipe, .roadmap, .rail-inner, .cat-card { background: var(--panel); border: 1px solid var(--rule); }
.page-index .article-head, .page-guide .article-head { background: none; }
.prose a { text-decoration: underline; text-decoration-color: var(--faint); text-underline-offset: 3px; }
.prose a:hover { text-decoration-color: var(--ink); }
.article-head h1, .prose h2, .prose h3, .block-title, .rm-track-name, .cat-card strong, .kb-area-name strong { letter-spacing: -.02em; font-weight: 600; }
.article-body blockquote::before { display: none; }

/* ======================================================================
   Dawn. Black on white was tiring to read for long: the whole palette is
   warmed a step towards first light (a warm near-black, unbleached ink, an
   amber accent), the leading and margins are opened up, and a low sunrise
   glow sits under long pages. Colour lives here; the block above only sets
   radii and hairlines.
   ====================================================================== */
:root {
  --paper: #0C0A08; --panel: #14110E;
  --ink: #EFE6DA; --ink-soft: #D6CCBF; --muted: #A59A8C; --faint: #6F665C;
  --rule: #27221D; --rule-soft: #1B1714;
  --link: #F2C39A; --link-hover: #FFD9B8;
  --ember: #E8A672; --ember-bg: rgba(232, 166, 114, .10);
  --code-bg: #17130F; --mark: rgba(242, 195, 154, .22);
}
:root[data-theme="light"] {
  --paper: #F5F5F2; --panel: #FDFDFB;
  --ink: #252A2D; --ink-soft: #414A50; --muted: #606A70; --faint: #636C71;
  --rule: #D9DEDD; --rule-soft: #E7EBE9;
  --link: #99512C; --link-hover: #773C20;
  --ember: #98512B; --ember-bg: rgba(152, 81, 43, .08);
  --code-bg: #ECEFEC; --mark: rgba(152, 81, 43, .14);
}
html.sky-back::after {
  content: ""; position: fixed; left: 0; right: 0; bottom: 0; height: 42vh; z-index: -1; pointer-events: none;
  background:
    radial-gradient(ellipse 62% 58% at 16% 108%, rgba(255, 168, 96, .17), rgba(255, 168, 96, 0) 70%),
    linear-gradient(to top, rgba(236, 150, 88, .09), rgba(236, 150, 88, .03) 48%, rgba(236, 150, 88, 0));
}
:root[data-theme="light"].sky-back::after { display: none; }
.hero-kicker { color: #D9CFC3; }
.hero-title { color: #F7F1E8; }
:root[data-theme="light"] .hero {
  background:
    radial-gradient(ellipse 85% 55% at 15% 100%, rgba(224, 199, 165, .18), transparent 75%),
    linear-gradient(to top, #E3E9EC, var(--paper) 68%);
}
:root[data-theme="light"] .hero::before { display: none; }
:root[data-theme="light"] .hero-kicker { color: var(--muted); }
:root[data-theme="light"] .hero-title { color: var(--ink); text-shadow: none; }
:root[data-theme="light"] .hero-scroll { border-color: var(--muted); }
:root[data-theme="light"] .topbar {
  background: color-mix(in srgb, var(--paper) 96%, transparent);
  backdrop-filter: blur(10px);
}

/* reading rhythm */
body { line-height: 1.85; }
html.lang-zh body { letter-spacing: 0; }
.shell { gap: 0 3.25rem; }
main { padding: 2.6rem 0 6rem; }
.prose { max-width: 42rem; }
.prose p { margin: 0 0 1.35rem; }
.prose > p:first-of-type { font-size: 1.1rem; line-height: 1.8; }
.prose h2 { font-size: 1.45rem; line-height: 1.3; margin: 3.4rem 0 1.1rem; padding-top: 1.4rem; }
.prose h3 { font-size: 1.12rem; margin: 2.4rem 0 .7rem; }
.prose h4 { margin: 1.8rem 0 .5rem; }
.prose ul, .prose ol { margin: 0 0 1.4rem; padding-left: 1.5rem; }
.prose li { margin-bottom: .55rem; }
.prose li > ul, .prose li > ol { margin: .5rem 0 .3rem; }
html.lang-zh :is(.prose, .article-body) > :is(p, ul, ol, blockquote) { line-height: 1.95; line-break: strict; word-break: normal; }
html.lang-zh :is(.article-head h1, .prose h1, .prose h2, .prose h3, .prose h4) { letter-spacing: 0; line-height: 1.5; line-break: strict; word-break: normal; }
html.lang-zh .article-head h1 { max-width: 100%; text-wrap: pretty; }
.page-home .article-body table { width: 100%; min-width: 0; table-layout: fixed; }
.page-home .article-body th { white-space: normal; text-transform: none; letter-spacing: 0; }
.page-home .article-body th:first-child { width: 32%; }
.page-home .article-body :is(th, td) { overflow-wrap: anywhere; }
.page-home .article-body td a { white-space: normal; }
.prose .algorithm-trace table { width: 100%; min-width: 0; table-layout: fixed; }
.prose .algorithm-trace :is(th, td) { overflow-wrap: anywhere; font-variant-numeric: tabular-nums; }
.prose .algorithm-trace th { white-space: normal; text-transform: none; letter-spacing: 0; }
@media (max-width: 620px) {
  .page-home .article-body :is(th, td) { padding: .8rem .55rem; font-size: .85rem; line-height: 1.75; }
  .prose .algorithm-trace :is(th, td) { padding: .65rem .3rem; font-size: .8rem; line-height: 1.5; }
}
.prose blockquote { margin: 1.7rem 0; padding: .25rem 0 .25rem 1.2rem; border-left: 2px solid color-mix(in srgb, var(--ember) 60%, transparent); }
.prose hr { margin: 3.2rem 0; }
.prose pre { padding: 1.1rem 1.2rem; margin: 1.7rem 0; font-size: .84rem; line-height: 1.7; }
.prose table { font-size: .9rem; }
.prose th { padding: .55rem .8rem; }
.prose td { padding: .62rem .8rem; }
.prose figure, .prose p > img { margin: 2rem 0; }
.prose details { margin: 1.7rem 0; }
.prose details > summary { padding: .8rem 1rem; line-height: 1.5; }
.prose details > *:not(summary) { margin-left: 1rem; margin-right: 1rem; }
.prose details > *:nth-child(2) { margin-top: 1rem; }
.prose details > *:last-child { margin-bottom: 1rem; }
.katex-display { margin: 1.5rem 0; padding: .7rem 0; }
.lesson-recipe { margin: 2rem 0 2.6rem; }
.lesson-recipe > div { padding: 1rem 1.1rem 1.05rem 1.25rem; min-height: 5.6rem; }
.lesson-recipe > div::before { background: color-mix(in srgb, var(--ember) 70%, transparent); }
.lesson-recipe span { margin-bottom: .4rem; }
.lesson-recipe strong { font-size: .92rem; line-height: 1.55; font-weight: 500; }
.taste-check { margin: 1.8rem 0 2.2rem; padding: 1.05rem 1.15rem 1rem 1.3rem; }
.taste-check li { margin-bottom: .45rem; line-height: 1.65; }
.article-head { margin-bottom: 2.4rem; }

/* quieter chrome around the text */
.side { padding: 2rem .75rem 3rem 0; }
.nav .sec > ul > li > a { padding: .3rem .55rem .3rem .75rem; font-size: .84rem; line-height: 1.5; color: var(--muted); }
.nav .sec > ul > li > a:hover { color: var(--ink); }
.nav .sec { margin-bottom: 1rem; }
.rail { padding: 2.6rem 0 3rem; }
.toc li a { padding: .28rem 0 .28rem .75rem; font-size: .78rem; line-height: 1.45; }
.toc li.l3 { display: none; }
.topbar { border-bottom-color: var(--rule-soft); }

/* -------- share-ready polish: the strip, the head on phones, the home measure -------- */
.subtabs-label { flex: none; }
.article-head h1 { max-width: 18ch; font-size: clamp(2.1rem, 1.2rem + 2.4vw, 3.4rem); line-height: 1.1; }
.chapter-mark { font-size: 7rem; }
@media (max-width: 1080px) {
  /* the direction strip scrolls on narrow screens; fade the edges so the cut-off text reads as "more" */
  .topbar-tabs { padding: 0 .2rem;
    -webkit-mask-image: linear-gradient(90deg, transparent, #000 12px, #000 calc(100% - 12px), transparent);
    mask-image: linear-gradient(90deg, transparent, #000 12px, #000 calc(100% - 12px), transparent); }
}
@media (max-width: 620px) {
  .topbar { gap: .45rem; padding: 0 .65rem; }
  .topbar-tabs a { padding: 0 .55rem; }
  .topbar-tabs a::after { left: .55rem; right: .55rem; }
  .topbar-tabs a span { font-size: .86rem; }
  .topbar-tabs .tab-sep { margin: 0 .2rem; }
  .article-head { margin-bottom: 2rem; padding: .5rem 0 1.5rem 1rem; }
  .article-head h1 { font-size: clamp(1.7rem, 6.8vw, 2rem); max-width: none; letter-spacing: -.03em; line-height: 1.18; }
  .chapter-mark { font-size: 5rem; top: -.35rem; }
  .article-meta { margin-top: .9rem; }
}

/* -------- sidebar: a block, then short entries under it ----------------------------------
   The block (group) names the topic; entries are short labels hanging off one guide line,
   the full title shows on hover. Section headings appear only inside mixed blocks. */
.nav .cat { margin: 1.5rem 0 .5rem; padding: 0 .6rem; }
.nav .cat:first-child { margin-top: .3rem; }
.nav .cat a, .nav .cat span { font: 650 .64rem/1 var(--sans); letter-spacing: .15em; text-transform: uppercase; color: var(--ember); text-decoration: none; }
.nav .grp + .grp { margin-top: .15rem; }
.nav details > summary {
  padding: .45rem .6rem .45rem .45rem; gap: .5rem; border-radius: 7px;
  font: 600 .9rem/1.3 var(--sans), var(--cjk); letter-spacing: -.005em; text-transform: none; color: var(--ink-soft);
}
.nav details > summary:hover { background: var(--rule-soft); color: var(--ink); }
.nav details[open] > summary, .nav details:has(a.active) > summary { color: var(--ink); }
.nav details > summary .chev { color: var(--faint); }
.nav details[open] > summary .chev { color: var(--ember); }
.grp-count { font: .66rem/1 var(--mono); color: var(--faint); }
.grp-body { margin: .1rem 0 .7rem 1.05rem; padding: .1rem 0; border-left: 1px solid var(--rule); }
.nav .sec { margin: 0; }
.nav .sec + .sec { margin-top: .5rem; }
.nav .sec-flat + .sec-flat { margin-top: 0; }
.nav .sec-num { display: none; }
.nav .sec-name {
  display: block; padding: .3rem .8rem .2rem; font: 650 .62rem/1.2 var(--sans), var(--cjk);
  letter-spacing: .13em; text-transform: uppercase; color: var(--faint);
}
.nav .sec > ul { margin: 0; }
.nav .sec:not(.sec-flat) > ul { margin-left: .55rem; }
.nav .sec > ul > li > a {
  display: block; margin-left: -1px; padding: .3rem .7rem .3rem .8rem;
  font-size: .87rem; line-height: 1.4; color: var(--muted); text-decoration: none;
  white-space: nowrap; overflow: hidden; text-overflow: ellipsis;
  border-left: 2px solid transparent; border-radius: 0 6px 6px 0;
}
.nav .sec > ul > li > a:hover { color: var(--ink); background: var(--rule-soft); }
.nav .sec > ul > li > a.active { color: var(--ink); font-weight: 600; background: var(--ember-bg); border-left-color: var(--ember); }
.subtabs { gap: .3rem; }
.subtabs-label { margin-right: .25rem; }
.subtabs a { padding: .34rem .66rem; }
/* the home page is one short read now: same measure as a note */
.page-home .prose, .page-home .page-foot { max-width: 42rem; }
/* a note without section headings has nothing to list: no empty "on this page" box */
.rail-inner:not(:has(.toc a)) { display: none; }

/* ======================================================================
   Tables, read at a glance
   The notes compare things constantly, so a table is usually the argument
   itself. Give the rows room, let the first column read as the label it is,
   and let a wide table scroll on a phone instead of squeezing six columns
   into 320 pixels.
   ====================================================================== */
.prose table { line-height: 1.6; }
.prose th { padding-top: .5rem; padding-bottom: .5rem; }
.prose td { padding: .72rem .85rem; }
.prose td:first-child { color: var(--ink); font-weight: 550; }
.prose tbody tr:nth-child(even) { background: color-mix(in srgb, var(--rule-soft) 45%, transparent); }
.prose tbody tr:hover { background: color-mix(in srgb, var(--ember) 9%, transparent); }
.prose table code { white-space: nowrap; }
@media (max-width: 720px) {
  .prose table { min-width: 32rem; }          /* the wrapper scrolls; cells stay readable */
  .prose td { padding: .62rem .7rem; }
  .prose .compact-table table { min-width: 0; table-layout: fixed; }
  .prose .compact-table :is(th, td) { padding: .6rem .4rem; }
  .prose .compact-table th { white-space: normal; letter-spacing: 0; overflow-wrap: anywhere; }
}

/* ======================================================================
   Study notes in two zones: Quant Researcher and AI / ML Engineer are
   tested on different things, so each gets its own row of blocks and its
   own run of the sidebar.
   ====================================================================== */
.subtabs.has-zones { flex-direction: column; align-items: stretch; gap: .55rem; }
.subtabs-zone { display: grid; grid-template-columns: 10.2rem 1fr; align-items: start; gap: .35rem; }
.subtabs-pills { display: flex; flex-wrap: wrap; gap: .35rem; }
.has-zones .subtabs-label { padding-top: .5rem; white-space: nowrap; }
.nav .zone { list-style: none; margin: .9rem 0 .25rem; padding: .55rem .55rem 0; border-top: 1px solid var(--rule-soft); }
.nav .cat + .zone { margin-top: .2rem; padding-top: 0; border-top: 0; }
.nav .zone span {
  font-family: var(--sans), var(--cjk); font-size: .64rem; font-weight: 650; letter-spacing: .08em;
  text-transform: uppercase; color: var(--muted);
}
@media (max-width: 760px) {
  .subtabs.has-zones { overflow: visible; }
  .subtabs-zone { grid-template-columns: 1fr; gap: .3rem; }
  .subtabs-pills { flex-wrap: nowrap; overflow-x: auto; scrollbar-width: none; }
  .subtabs-pills::-webkit-scrollbar { display: none; }
  .has-zones .subtabs-label { padding-top: 0; }
}