:root {
  --bg: #f7f8fa;
  --bg-panel: #ffffff;
  --bg-soft: #f0f2f5;
  --text: #1f2430;
  --text-soft: #5b6472;
  --text-faint: #8a93a3;
  --border: #e3e7ee;
  --accent: #2f6fed;
  --accent-soft: #eaf1ff;
  --accent-text: #1d4fbf;
  --green: #17a673;
  --green-soft: #e6f7f0;
  --amber: #d97706;
  --amber-soft: #fdf3e3;
  --red: #dc2626;
  --red-soft: #fdecec;
  --purple: #7c3aed;
  --purple-soft: #f1ebfe;
  --code-bg: #f2f4f8;
  --shadow: 0 1px 3px rgba(16, 24, 40, .06), 0 8px 24px rgba(16, 24, 40, .06);
  --sidebar-w: 288px;
  --toc-w: 232px;
  --topbar-h: 58px;
  --radius: 12px;
}

html[data-theme="dark"] {
  --bg: #0f1218;
  --bg-panel: #161b24;
  --bg-soft: #1d2430;
  --text: #e6e9f0;
  --text-soft: #a7b0c0;
  --text-faint: #6d7789;
  --border: #262e3c;
  --accent: #5b8df6;
  --accent-soft: #1b2740;
  --accent-text: #8fb2ff;
  --green: #34d399;
  --green-soft: #10281f;
  --amber: #fbbf24;
  --amber-soft: #2b2210;
  --red: #f87171;
  --red-soft: #2c1516;
  --purple: #a78bfa;
  --purple-soft: #211a36;
  --code-bg: #1b2130;
  --shadow: 0 1px 3px rgba(0, 0, 0, .4), 0 8px 24px rgba(0, 0, 0, .35);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  font-size: 15.5px;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
}

/* ---------- Topbar ---------- */
.topbar {
  position: fixed;
  top: 0; left: 0; right: 0;
  height: var(--topbar-h);
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 0 18px;
  background: color-mix(in srgb, var(--bg-panel) 88%, transparent);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  z-index: 50;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--text);
  font-weight: 700;
  white-space: nowrap;
}
.brand-mark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 34px; height: 34px;
  border-radius: 9px;
  background: linear-gradient(135deg, var(--accent), var(--purple));
  color: #fff;
  font-size: 12.5px;
  font-weight: 800;
  letter-spacing: .5px;
}
.brand-text { font-size: 15.5px; }

.topbar-search {
  flex: 1;
  max-width: 520px;
  margin-left: auto;
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 7px 12px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: 10px;
  color: var(--text-faint);
  transition: border-color .15s, box-shadow .15s;
}
.topbar-search:focus-within {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-soft);
}
.topbar-search input {
  flex: 1;
  border: none;
  outline: none;
  background: transparent;
  color: var(--text);
  font-size: 14px;
  font-family: inherit;
}
.topbar-search kbd {
  font-size: 11px;
  padding: 1px 6px;
  border: 1px solid var(--border);
  border-bottom-width: 2px;
  border-radius: 5px;
  color: var(--text-faint);
  background: var(--bg-panel);
}

.icon-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 36px; height: 36px;
  border: 1px solid transparent;
  border-radius: 9px;
  background: transparent;
  color: var(--text-soft);
  cursor: pointer;
  transition: background .15s, color .15s;
}
.icon-btn:hover { background: var(--bg-soft); color: var(--text); }
.icon-btn.small { width: 28px; height: 28px; }

#menuToggle { display: none; }

html[data-theme="light"] .icon-moon { display: none; }
html[data-theme="dark"] .icon-sun { display: none; }

/* ---------- Layout ---------- */
.layout {
  display: flex;
  padding-top: var(--topbar-h);
  min-height: 100vh;
}

.sidebar {
  position: fixed;
  top: var(--topbar-h);
  bottom: 0;
  left: 0;
  width: var(--sidebar-w);
  overflow-y: auto;
  padding: 18px 14px 24px;
  background: var(--bg-panel);
  border-right: 1px solid var(--border);
  z-index: 40;
}

.progress-card {
  padding: 12px 14px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg-soft);
  margin-bottom: 16px;
}
.progress-head {
  display: flex;
  justify-content: space-between;
  font-size: 12.5px;
  color: var(--text-soft);
  margin-bottom: 8px;
  font-weight: 600;
}
.progress-bar {
  height: 7px;
  border-radius: 99px;
  background: var(--border);
  overflow: hidden;
}
.progress-fill {
  height: 100%;
  width: 0;
  border-radius: 99px;
  background: linear-gradient(90deg, var(--accent), var(--purple));
  transition: width .3s ease;
}

.chapter-nav { display: flex; flex-direction: column; gap: 2px; }

.nav-group-label {
  font-size: 11.5px;
  font-weight: 700;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--text-faint);
  padding: 14px 10px 6px;
}

.nav-item {
  display: flex;
  align-items: center;
  gap: 9px;
  padding: 8px 10px;
  border-radius: 9px;
  text-decoration: none;
  color: var(--text-soft);
  font-size: 13.8px;
  line-height: 1.4;
  transition: background .12s, color .12s;
}
.nav-item:hover { background: var(--bg-soft); color: var(--text); }
.nav-item.active {
  background: var(--accent-soft);
  color: var(--accent-text);
  font-weight: 600;
}
.nav-num {
  flex: none;
  width: 22px; height: 22px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 6px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  font-size: 11px;
  font-weight: 700;
  color: var(--text-faint);
}
.nav-item.active .nav-num {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}
.nav-check {
  margin-left: auto;
  color: var(--green);
  flex: none;
  opacity: 0;
  transition: opacity .2s;
}
.nav-item.done .nav-check { opacity: 1; }
.nav-item.done .nav-title { color: var(--text-faint); }
.nav-item.done.active .nav-title { color: var(--accent-text); }

.sidebar-foot {
  margin-top: 18px;
  padding: 10px;
  border-top: 1px dashed var(--border);
}
.link-btn {
  background: none;
  border: none;
  color: var(--text-faint);
  font-size: 12.5px;
  cursor: pointer;
  padding: 4px 6px;
  border-radius: 6px;
  font-family: inherit;
}
.link-btn:hover { color: var(--red); background: var(--red-soft); }

/* ---------- Content ---------- */
.content {
  flex: 1;
  min-width: 0;
  margin-left: var(--sidebar-w);
  margin-right: var(--toc-w);
  padding: 34px 46px 90px;
  max-width: 900px;
}

.loading {
  color: var(--text-faint);
  padding: 60px 0;
  text-align: center;
}

.chapter-head { margin-bottom: 28px; }
.chapter-eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 12px;
  font-weight: 700;
  letter-spacing: .05em;
  color: var(--accent-text);
  background: var(--accent-soft);
  padding: 3px 11px;
  border-radius: 99px;
  margin-bottom: 14px;
}
.chapter-title {
  font-size: 30px;
  line-height: 1.3;
  margin: 0 0 10px;
  font-weight: 800;
  letter-spacing: -.01em;
}
.chapter-desc {
  color: var(--text-soft);
  font-size: 15px;
  margin: 0;
}
.chapter-meta {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-top: 16px;
  flex-wrap: wrap;
}
.btn {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding: 7px 14px;
  border-radius: 9px;
  border: 1px solid var(--border);
  background: var(--bg-panel);
  color: var(--text-soft);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  font-family: inherit;
  transition: all .15s;
}
.btn:hover { border-color: var(--accent); color: var(--accent-text); }
.btn.primary {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}
.btn.primary:hover { filter: brightness(1.08); color: #fff; }
.btn.done {
  background: var(--green-soft);
  border-color: var(--green);
  color: var(--green);
}
.chapter-source {
  font-size: 12.5px;
  color: var(--text-faint);
}

/* ---------- Markdown body ---------- */
.md { font-size: 15.5px; }
.md > *:first-child { margin-top: 0; }

.md h2 {
  font-size: 22px;
  font-weight: 750;
  margin: 42px 0 14px;
  padding-bottom: 9px;
  border-bottom: 1px solid var(--border);
  scroll-margin-top: 76px;
}
.md h2::before {
  content: "";
  display: inline-block;
  width: 4px; height: 19px;
  border-radius: 3px;
  background: linear-gradient(180deg, var(--accent), var(--purple));
  margin-right: 10px;
  vertical-align: -3px;
}
.md h3 {
  font-size: 17.5px;
  font-weight: 700;
  margin: 30px 0 10px;
  color: var(--text);
  scroll-margin-top: 76px;
}
.md h4 {
  font-size: 15.5px;
  font-weight: 700;
  margin: 22px 0 8px;
  color: var(--text-soft);
}
.md p { margin: 12px 0; }
.md a { color: var(--accent-text); text-decoration: none; border-bottom: 1px solid color-mix(in srgb, var(--accent) 40%, transparent); }
.md a:hover { border-bottom-color: var(--accent); }

.md ul, .md ol { padding-left: 24px; margin: 12px 0; }
.md li { margin: 5px 0; }
.md li > ul, .md li > ol { margin: 4px 0; }

.md strong { font-weight: 700; }
.md em { font-style: normal; color: var(--amber); font-weight: 600; }

.md blockquote {
  margin: 18px 0;
  padding: 12px 18px;
  border-left: 4px solid var(--accent);
  background: var(--accent-soft);
  border-radius: 0 10px 10px 0;
  color: var(--text);
  font-size: 14.5px;
}
.md blockquote p { margin: 5px 0; }
.md blockquote strong:first-child { color: var(--accent-text); }

.md code {
  font-family: "SF Mono", ui-monospace, Menlo, Consolas, monospace;
  font-size: 13.5px;
  background: var(--code-bg);
  border: 1px solid var(--border);
  padding: 1.5px 6px;
  border-radius: 6px;
  color: var(--purple);
}
.md pre {
  margin: 16px 0;
  padding: 15px 18px;
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow-x: auto;
  line-height: 1.6;
}
.md pre code {
  background: none;
  border: none;
  padding: 0;
  color: var(--text);
  font-size: 13px;
}

.md table {
  width: 100%;
  border-collapse: collapse;
  margin: 18px 0;
  font-size: 14px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
}
.md th {
  background: var(--bg-soft);
  font-weight: 700;
  text-align: left;
  padding: 9px 13px;
  border-bottom: 1px solid var(--border);
  white-space: nowrap;
}
.md td {
  padding: 9px 13px;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}
.md tr:last-child td { border-bottom: none; }
.md tr:nth-child(even) td { background: color-mix(in srgb, var(--bg-soft) 45%, transparent); }

.md hr { border: none; border-top: 1px solid var(--border); margin: 32px 0; }

.math-display {
  margin: 18px 0;
  overflow-x: auto;
  overflow-y: hidden;
  padding: 4px 0;
  text-align: center;
}
.math-inline { padding: 0 1px; }
.katex { font-size: 1.05em; }
.md pre .katex, .md code .katex { font-size: 1em; }

/* Callout boxes */
.callout {
  margin: 20px 0;
  padding: 14px 18px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  font-size: 14.5px;
}
.callout p { margin: 6px 0; }
.callout-title { font-weight: 750; margin-bottom: 4px; display: flex; align-items: center; gap: 8px; }
.callout.tip { background: var(--green-soft); border-color: color-mix(in srgb, var(--green) 35%, transparent); }
.callout.tip .callout-title { color: var(--green); }
.callout.warn { background: var(--amber-soft); border-color: color-mix(in srgb, var(--amber) 35%, transparent); }
.callout.warn .callout-title { color: var(--amber); }
.callout.key { background: var(--purple-soft); border-color: color-mix(in srgb, var(--purple) 35%, transparent); }
.callout.key .callout-title { color: var(--purple); }
.callout.note { background: var(--accent-soft); border-color: color-mix(in srgb, var(--accent) 35%, transparent); }
.callout.note .callout-title { color: var(--accent-text); }

/* Chapter footer nav */
.chapter-footer {
  display: flex;
  justify-content: space-between;
  gap: 14px;
  margin-top: 54px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}
.footer-link {
  flex: 1;
  display: block;
  padding: 13px 16px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  text-decoration: none;
  color: var(--text);
  transition: border-color .15s, transform .15s;
  background: var(--bg-panel);
}
.footer-link:hover { border-color: var(--accent); transform: translateY(-1px); }
.footer-link.next { text-align: right; }
.footer-link .fl-label { font-size: 11.5px; color: var(--text-faint); display: block; margin-bottom: 3px; font-weight: 600; }
.footer-link .fl-title { font-size: 14px; font-weight: 650; }

/* ---------- TOC ---------- */
.toc-panel {
  position: fixed;
  top: var(--topbar-h);
  right: 0;
  bottom: 0;
  width: var(--toc-w);
  padding: 26px 16px;
  overflow-y: auto;
  border-left: 1px solid var(--border);
  background: var(--bg);
}
.toc-title {
  font-size: 12px;
  font-weight: 700;
  letter-spacing: .06em;
  color: var(--text-faint);
  text-transform: uppercase;
  margin-bottom: 12px;
  padding-left: 10px;
}
#tocNav { display: flex; flex-direction: column; gap: 1px; border-left: 2px solid var(--border); }
.toc-link {
  display: block;
  padding: 4px 10px;
  margin-left: -2px;
  border-left: 2px solid transparent;
  color: var(--text-soft);
  text-decoration: none;
  font-size: 12.8px;
  line-height: 1.5;
  transition: color .12s, border-color .12s;
}
.toc-link:hover { color: var(--text); }
.toc-link.active { color: var(--accent-text); border-left-color: var(--accent); font-weight: 600; }
.toc-link.lv3 { padding-left: 22px; font-size: 12.2px; }

/* ---------- Search results ---------- */
.search-results {
  position: fixed;
  top: var(--topbar-h);
  left: 0; right: 0; bottom: 0;
  background: color-mix(in srgb, var(--bg) 75%, transparent);
  backdrop-filter: blur(6px);
  z-index: 60;
  overflow-y: auto;
  padding: 26px 20px;
}
.search-results-inner {
  max-width: 760px;
  margin: 0 auto;
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 16px;
  box-shadow: var(--shadow);
  overflow: hidden;
}
.search-results-head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 14px 20px;
  border-bottom: 1px solid var(--border);
  font-size: 13.5px;
  color: var(--text-soft);
  font-weight: 600;
}
.search-list { padding: 8px; }
.search-hit {
  display: block;
  padding: 12px 14px;
  border-radius: 10px;
  text-decoration: none;
  color: var(--text);
  transition: background .12s;
}
.search-hit:hover { background: var(--bg-soft); }
.search-hit .hit-chapter {
  font-size: 11.5px;
  font-weight: 700;
  color: var(--accent-text);
  margin-bottom: 3px;
}
.search-hit .hit-snippet { font-size: 13.5px; color: var(--text-soft); line-height: 1.55; }
.search-hit mark { background: color-mix(in srgb, var(--amber) 35%, transparent); color: inherit; border-radius: 3px; padding: 0 2px; }
.search-empty { padding: 40px; text-align: center; color: var(--text-faint); }

/* ---------- Overlay & mobile ---------- */
.overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,.4);
  z-index: 39;
}
.overlay.show { display: block; }

.back-top {
  position: fixed;
  right: 22px;
  bottom: 26px;
  width: 42px; height: 42px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: var(--bg-panel);
  color: var(--text-soft);
  box-shadow: var(--shadow);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 30;
}
.back-top:hover { color: var(--accent); border-color: var(--accent); }

@media (max-width: 1180px) {
  .toc-panel { display: none; }
  .content { margin-right: 0; }
}

@media (max-width: 860px) {
  #menuToggle { display: inline-flex; }
  .brand-text { display: none; }
  .sidebar {
    transform: translateX(-100%);
    transition: transform .22s ease;
    box-shadow: var(--shadow);
  }
  .sidebar.open { transform: translateX(0); }
  .content { margin-left: 0; padding: 24px 20px 80px; }
  .chapter-title { font-size: 24px; }
  .topbar-search kbd { display: none; }
}

/* Print */
@media print {
  .topbar, .sidebar, .toc-panel, .chapter-footer, .back-top, .overlay { display: none !important; }
  .content { margin: 0; padding: 0; max-width: none; }
}

/* ============================================================
   Teaching components (Phase 1)
   ============================================================ */

:root {
  --yellow: #b7791f;
  --yellow-soft: #fdf6e3;
}
html[data-theme="dark"] {
  --yellow: #ecc94b;
  --yellow-soft: #2b2410;
}

/* ---------- Colored boxes ---------- */
.box {
  margin: 18px 0;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
}
.box-title {
  padding: 9px 16px;
  font-weight: 700;
  font-size: 13.5px;
  display: flex;
  align-items: center;
  gap: 8px;
  border-bottom: 1px solid color-mix(in srgb, currentColor 18%, transparent);
}
.box-body { padding: 12px 18px 14px; font-size: 14.8px; }
.box-body > *:first-child { margin-top: 0; }
.box-body > *:last-child { margin-bottom: 0; }
.box-body .md-inner > *:first-child { margin-top: 0; }

.box-intuition { background: var(--green-soft); border-color: color-mix(in srgb, var(--green) 35%, transparent); }
.box-intuition .box-title { color: var(--green); }
.box-example { background: var(--green-soft); border-color: color-mix(in srgb, var(--green) 30%, transparent); }
.box-example .box-title { color: var(--green); }
.box-math { background: var(--purple-soft); border-color: color-mix(in srgb, var(--purple) 32%, transparent); }
.box-math .box-title { color: var(--purple); }
.box-key { background: var(--purple-soft); border-color: color-mix(in srgb, var(--purple) 32%, transparent); }
.box-key .box-title { color: var(--purple); }
.box-engineering { background: var(--amber-soft); border-color: color-mix(in srgb, var(--amber) 35%, transparent); }
.box-engineering .box-title { color: var(--amber); }
.box-warning { background: var(--red-soft); border-color: color-mix(in srgb, var(--red) 35%, transparent); }
.box-warning .box-title { color: var(--red); }
.box-interview { background: var(--yellow-soft); border-color: color-mix(in srgb, var(--yellow) 40%, transparent); }
.box-interview .box-title { color: var(--yellow); }
.box-note { background: var(--accent-soft); border-color: color-mix(in srgb, var(--accent) 32%, transparent); }
.box-note .box-title { color: var(--accent-text); }

/* ---------- Foldable levels ---------- */
details.fold {
  margin: 16px 0;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg-panel);
  overflow: hidden;
}
details.fold > summary {
  padding: 11px 16px;
  cursor: pointer;
  font-weight: 650;
  font-size: 14px;
  display: flex;
  align-items: center;
  gap: 9px;
  list-style: none;
  user-select: none;
}
details.fold > summary::-webkit-details-marker { display: none; }
details.fold > summary::before {
  content: "▸";
  color: var(--text-faint);
  transition: transform .15s;
  font-size: 13px;
}
details.fold[open] > summary::before { transform: rotate(90deg); }
details.fold[open] > summary { border-bottom: 1px solid var(--border); }
.fold-body { padding: 6px 18px 14px; }
.fold-body > *:first-child { margin-top: 10px; }

details.answer {
  margin: 10px 0;
  border-left: 3px solid var(--yellow);
  background: color-mix(in srgb, var(--yellow-soft) 70%, transparent);
  border-radius: 0 8px 8px 0;
}
details.answer > summary {
  padding: 7px 14px;
  cursor: pointer;
  font-size: 13.5px;
  color: var(--yellow);
  font-weight: 650;
  list-style: none;
}
details.answer > summary::-webkit-details-marker { display: none; }
details.answer > summary::before { content: "▸ "; }
details.answer[open] > summary::before { content: "▾ "; }
.answer-body { padding: 2px 14px 10px; font-size: 14.2px; }
.answer-body > *:first-child { margin-top: 0; }

/* ---------- ShapeFlow ---------- */
.shapeflow { margin: 18px 0; display: flex; flex-direction: column; gap: 9px; }
.shape-row { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; }
.shape-part {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  padding: 6px 13px;
  border-radius: 10px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  min-width: 66px;
}
.shape-name { font-weight: 700; font-size: 13.5px; line-height: 1.3; }
.shape-dims { font-family: "SF Mono", ui-monospace, Menlo, monospace; font-size: 11px; color: var(--accent-text); margin-top: 2px; }
.shape-note { font-size: 11px; color: var(--text-faint); margin-top: 2px; }
.shape-op { color: var(--text-faint); font-weight: 700; font-size: 14px; }
.shape-arrow { color: var(--accent); font-weight: 800; font-size: 16px; }
.shape-part.result { background: var(--accent-soft); border-color: color-mix(in srgb, var(--accent) 45%, transparent); }

/* ---------- Demo blocks ---------- */
.demo-block {
  margin: 24px 0;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--bg-panel);
  box-shadow: var(--shadow);
  overflow: hidden;
}
.demo-head {
  padding: 10px 16px;
  font-weight: 700;
  font-size: 13.5px;
  background: var(--bg-soft);
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text-soft);
}
.demo-head .demo-tag {
  margin-left: auto;
  font-size: 11px;
  font-weight: 600;
  color: var(--accent-text);
  background: var(--accent-soft);
  padding: 2px 9px;
  border-radius: 99px;
}
.demo { padding: 16px; }
.demo-caption { padding: 11px 16px; font-size: 13px; color: var(--text-soft); border-top: 1px dashed var(--border); background: var(--bg); }
.demo-caption > *:first-child { margin-top: 0; }
.demo-caption > *:last-child { margin-bottom: 0; }
.demo-error { color: var(--red); font-size: 13px; }
.demo-sub { font-size: 13.5px; color: var(--text-soft); margin: 8px 0; }
.demo-sub b { color: var(--text); }

.demo-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 20px;
  align-items: center;
  margin-bottom: 14px;
}
.demo-control {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  color: var(--text-soft);
}
.demo-control input[type="range"] { width: 138px; accent-color: var(--accent); }
.demo-val {
  font-family: "SF Mono", ui-monospace, Menlo, monospace;
  font-size: 12.5px;
  color: var(--accent-text);
  min-width: 46px;
  text-align: right;
}
.demo-btn {
  padding: 5px 12px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg-panel);
  color: var(--text-soft);
  font-size: 12.8px;
  font-weight: 600;
  cursor: pointer;
  font-family: inherit;
  transition: all .14s;
}
.demo-btn:hover { border-color: var(--accent); color: var(--accent-text); }
.demo-btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
.demo-btn.primary:hover { filter: brightness(1.08); color: #fff; }
.demo-btn.active { background: var(--accent-soft); color: var(--accent-text); border-color: var(--accent); }
.demo-btn:disabled { opacity: .45; cursor: not-allowed; }
.demo-canvas { width: 100%; max-width: 560px; height: auto; display: block; margin: 0 auto; }
.demo-readout {
  font-family: "SF Mono", ui-monospace, Menlo, monospace;
  font-size: 12.8px;
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 9px;
  padding: 10px 13px;
  margin-top: 12px;
  line-height: 1.75;
  white-space: pre-wrap;
  overflow-x: auto;
}
.demo-grid2 { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; align-items: start; }
.demo-grid3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: 12px; align-items: start; }
.demo-panel { border: 1px solid var(--border); border-radius: 10px; padding: 10px 12px; background: var(--bg); }
.demo-panel h5 { margin: 0 0 8px; font-size: 12.5px; color: var(--text-faint); font-weight: 700; letter-spacing: .04em; text-transform: uppercase; }
.demo-num { width: 64px; padding: 4px 7px; border: 1px solid var(--border); border-radius: 7px; background: var(--bg); color: var(--text); font-family: inherit; font-size: 13px; }
.demo-num:focus { outline: none; border-color: var(--accent); }
.demo-chips { display: flex; flex-wrap: wrap; gap: 6px; margin: 10px 0; }
.chip {
  padding: 5px 11px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg-soft);
  font-size: 13px;
  cursor: pointer;
  color: var(--text-soft);
  transition: all .14s;
  font-family: inherit;
}
.chip:hover { border-color: var(--accent); color: var(--accent-text); }
.chip.on { background: var(--accent); border-color: var(--accent); color: #fff; font-weight: 600; }
.chip.ghost { cursor: default; }
.chip.ghost:hover { border-color: var(--border); color: var(--text-soft); }
.chip.green { background: var(--green-soft); border-color: var(--green); color: var(--green); }
.chip.red { background: var(--red-soft); border-color: var(--red); color: var(--red); }
.chip.amber { background: var(--amber-soft); border-color: var(--amber); color: var(--amber); }

/* ---------- Bars ---------- */
.bars { display: flex; flex-direction: column; gap: 7px; }
.bar-row { display: grid; grid-template-columns: 96px 1fr 74px; align-items: center; gap: 9px; font-size: 12.8px; }
.bar-label { color: var(--text-soft); overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.bar-track { height: 19px; background: var(--bg-soft); border-radius: 6px; overflow: hidden; border: 1px solid var(--border); }
.bar-fill { height: 100%; border-radius: 5px; background: linear-gradient(90deg, var(--accent), var(--purple)); transition: width .25s; }
.bar-fill.green { background: linear-gradient(90deg, #0e9f6e, var(--green)); }
.bar-fill.red { background: linear-gradient(90deg, #e02424, var(--red)); }
.bar-fill.amber { background: linear-gradient(90deg, #d97706, var(--amber)); }
.bar-fill.dim { background: var(--border); }
.bar-val { font-family: "SF Mono", ui-monospace, Menlo, monospace; font-size: 12px; text-align: right; color: var(--text-soft); }

/* ---------- Heatmap ---------- */
.heatmap { display: grid; gap: 3px; }
.heat-cell {
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 5px;
  font-size: 10.5px;
  font-family: "SF Mono", ui-monospace, Menlo, monospace;
  min-height: 28px;
  border: 1px solid transparent;
  color: var(--text);
}
.heat-cell.head { background: transparent; color: var(--text-faint); font-weight: 700; font-size: 11px; border: none; }

/* ---------- Matrices ---------- */
.mat-wrap { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; margin: 12px 0; }
.mat-group { display: flex; flex-direction: column; align-items: center; gap: 5px; }
.mat-label { font-size: 12.5px; font-weight: 700; color: var(--text-soft); }
.mat-label .mat-shape { font-weight: 500; color: var(--accent-text); font-family: "SF Mono", ui-monospace, Menlo, monospace; font-size: 11px; }
.mat { border-collapse: separate; border-spacing: 3px; }
.mat td {
  width: 46px; height: 34px;
  text-align: center;
  font-family: "SF Mono", ui-monospace, Menlo, monospace;
  font-size: 12.5px;
  border-radius: 6px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
}
.mat td.hl { background: var(--accent-soft); border-color: var(--accent); font-weight: 700; }
.mat td.neg { color: var(--red); }
.mat td.pos { color: var(--accent-text); }

/* ---------- Quiz ---------- */
.quiz {
  margin: 24px 0;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--bg-panel);
  padding: 16px 18px;
}
.quiz-head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-weight: 700;
  font-size: 13.5px;
  color: var(--yellow);
  margin-bottom: 10px;
  gap: 10px;
}
.quiz-status { font-size: 12.5px; font-weight: 600; }
.quiz-status.ok { color: var(--green); }
.quiz-status.no { color: var(--red); }
.quiz-question { font-weight: 650; margin-bottom: 12px; font-size: 15px; }
.quiz-options { display: flex; flex-direction: column; gap: 8px; }
.quiz-option {
  display: flex;
  gap: 10px;
  text-align: left;
  padding: 9px 13px;
  border-radius: 9px;
  border: 1px solid var(--border);
  background: var(--bg);
  cursor: pointer;
  font-size: 14px;
  font-family: inherit;
  color: var(--text);
  transition: all .14s;
  line-height: 1.6;
}
.quiz-option:hover { border-color: var(--accent); }
.quiz-option .quiz-key { font-weight: 700; color: var(--text-faint); flex: none; }
.quiz-option.correct { background: var(--green-soft); border-color: var(--green); }
.quiz-option.correct .quiz-key { color: var(--green); }
.quiz-option.wrong { background: var(--red-soft); border-color: var(--red); }
.quiz-option.wrong .quiz-key { color: var(--red); }
.quiz.answered .quiz-option { cursor: default; }
.quiz-explain {
  margin-top: 12px;
  padding: 11px 14px;
  background: var(--bg-soft);
  border-radius: 9px;
  font-size: 14px;
  border-left: 3px solid var(--accent);
}
.quiz-explain strong { color: var(--accent-text); }

/* ---------- Related knowledge tags ---------- */
.related {
  margin: 36px 0 0;
  padding: 16px 18px;
  border: 1px dashed var(--border);
  border-radius: var(--radius);
  background: var(--bg-soft);
}
.related-title { font-weight: 700; font-size: 13.5px; margin-bottom: 10px; color: var(--text-soft); display: flex; gap: 8px; align-items: center; }
.related-row { display: flex; gap: 10px; align-items: baseline; margin: 8px 0; flex-wrap: wrap; }
.related-label { font-size: 12.5px; color: var(--text-faint); flex: none; min-width: 66px; font-weight: 650; }
.tag {
  display: inline-block;
  padding: 3px 11px;
  border-radius: 99px;
  font-size: 12.5px;
  background: var(--bg-panel);
  border: 1px solid var(--border);
  color: var(--text-soft);
  text-decoration: none;
  transition: all .14s;
}
a.tag:hover { border-color: var(--accent); color: var(--accent-text); }
a.tag::after { content: " ↗"; font-size: 10px; color: var(--text-faint); }

/* ---------- Small layout helpers used by demos ---------- */
.demo-flex { display: flex; gap: 14px; flex-wrap: wrap; align-items: center; }
.demo-col { display: flex; flex-direction: column; gap: 10px; }
.demo-scroll { overflow-x: auto; }
.svg-demo { width: 100%; max-width: 560px; height: auto; display: block; margin: 0 auto; }
.stat-line { font-size: 13px; color: var(--text-soft); margin: 4px 0; }
.stat-line b { color: var(--text); font-family: "SF Mono", ui-monospace, Menlo, monospace; }
.badge {
  display: inline-block;
  padding: 1px 8px;
  border-radius: 99px;
  font-size: 11.5px;
  font-weight: 700;
  background: var(--accent-soft);
  color: var(--accent-text);
}
.badge.green { background: var(--green-soft); color: var(--green); }
.badge.red { background: var(--red-soft); color: var(--red); }
.badge.gray { background: var(--bg-soft); color: var(--text-faint); }

@media (max-width: 640px) {
  .demo-grid2, .demo-grid3 { grid-template-columns: 1fr; }
  .bar-row { grid-template-columns: 76px 1fr 62px; }
  .mat td { width: 38px; height: 30px; font-size: 11.5px; }
}