/* ============================================================
   Từ que đo đến lượng tử hấp dẫn
   Design system: paper-and-ink reading + observatory lab
   ============================================================ */

:root {
  --topbar-h: 66px;
  --sidebar-w: 312px;
  --reading-scale: 1;
  --serif: "Iowan Old Style", "Palatino Linotype", "Noto Serif", "DejaVu Serif", "Times New Roman", serif;
  --sans: "Inter", "Segoe UI", "Noto Sans", "DejaVu Sans", system-ui, -apple-system, sans-serif;
  --mono: "JetBrains Mono", "SFMono-Regular", "Cascadia Code", Consolas, monospace;

  --bg: #f6f1e6;
  --bg-soft: #efe8d9;
  --surface: #fffdf8;
  --surface-2: #f4eddf;
  --surface-3: #ebe2d0;
  --ink: #18212f;
  --ink-2: #344054;
  --muted: #667085;
  --line: #ddd2be;
  --line-strong: #c9bca4;
  --accent: #0d6b63;
  --accent-ink: #064e48;
  --accent-soft: #dff0ec;
  --amber: #a85a06;
  --amber-soft: #fdf0d2;
  --indigo: #3b3f8f;
  --indigo-soft: #e8e9fb;
  --danger: #a1281d;
  --danger-soft: #fbe7e3;
  --ok: #17663a;
  --ok-soft: #e2f3e8;
  --repo-bg: #0d1d30;
  --repo-bg-2: #12283f;
  --repo-ink: #d9e8ff;
  --repo-dim: #93a9c4;
  --repo-line: #284566;
  --repo-accent: #ffc56e;

  --lab-bg: #f8f3e8;
  --lab-bg-2: #efe7d7;
  --lab-ink: #18212f;
  --lab-dim: #5b6b82;
  --lab-line: #d8cbb4;
  --lab-cyan: #0b6b7a;
  --lab-amber: #a85a06;
  --lab-pink: #b4236b;
  --lab-green: #17663a;
  --lab-violet: #4b3fa0;
  --lab-red: #a1281d;

  --shadow-sm: 0 1px 2px rgba(24, 33, 47, .06), 0 2px 8px rgba(24, 33, 47, .04);
  --shadow-md: 0 8px 30px rgba(24, 33, 47, .09);
  --shadow-lg: 0 24px 70px rgba(24, 33, 47, .16);
  --radius: 14px;
  --radius-sm: 9px;
  --ease: cubic-bezier(.2, .7, .2, 1);
}

[data-theme="dark"] {
  --bg: #0b0f16;
  --bg-soft: #0f1520;
  --surface: #111925;
  --surface-2: #162130;
  --surface-3: #1d2a3b;
  --ink: #e7edf7;
  --ink-2: #c3cedd;
  --muted: #91a0b5;
  --line: #263447;
  --line-strong: #354960;
  --accent: #5ed6c5;
  --accent-ink: #9df0e3;
  --accent-soft: #12332f;
  --amber: #f1b35e;
  --amber-soft: #332612;
  --indigo: #a7abff;
  --indigo-soft: #1d2144;
  --danger: #ff8d82;
  --danger-soft: #3a1c19;
  --ok: #7ce0a7;
  --ok-soft: #123222;
  --repo-bg: #0a1727;
  --repo-bg-2: #0f2137;
  --repo-ink: #d9e8ff;
  --repo-dim: #8fa6c1;
  --repo-line: #233f5e;
  --lab-bg: #07101c;
  --lab-bg-2: #0b1727;
  --lab-ink: #dce9fb;
  --lab-dim: #8fa6c4;
  --lab-line: #1d3550;
  --lab-cyan: #4dd6ff;
  --lab-amber: #ffb454;
  --lab-pink: #ff7aa8;
  --lab-green: #5ee6a8;
  --lab-violet: #b49cff;
  --lab-red: #ff6470;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, .3);
  --shadow-md: 0 10px 34px rgba(0, 0, 0, .38);
  --shadow-lg: 0 30px 80px rgba(0, 0, 0, .5);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: .001ms !important; transition-duration: .001ms !important; }
}
html, body { overflow-x: clip; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.6;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}
body.no-scroll { overflow: hidden; }
img, svg, canvas { max-width: 100%; }
a { color: var(--accent); text-decoration-thickness: .08em; text-underline-offset: .18em; }
a:hover { color: var(--accent-ink); }
button { font: inherit; color: inherit; }
kbd {
  font-family: var(--mono); font-size: .78em; padding: .12em .38em;
  border: 1px solid var(--line-strong); border-bottom-width: 2px; border-radius: 5px;
  background: var(--surface); color: var(--ink-2);
}
::selection { background: color-mix(in srgb, var(--accent) 25%, transparent); }
:focus-visible { outline: 2.5px solid var(--amber); outline-offset: 3px; border-radius: 4px; }

.sr-only {
  position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0;
}
.skip-link {
  position: fixed; left: 12px; top: -80px; z-index: 200; background: var(--ink); color: var(--bg);
  padding: 10px 16px; border-radius: 8px; text-decoration: none; transition: top .18s var(--ease);
}
.skip-link:focus { top: 10px; color: var(--bg); }

/* ---------- top bar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 60;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(14px) saturate(1.2);
  -webkit-backdrop-filter: blur(14px) saturate(1.2);
}
.topbar-inner {
  height: var(--topbar-h); max-width: 1560px; margin: 0 auto;
  padding: 0 clamp(14px, 2.4vw, 30px);
  display: flex; align-items: center; gap: 24px;
}
.brand { display: flex; align-items: center; gap: 11px; text-decoration: none; color: var(--ink); flex: 0 0 auto; }
.brand-mark { color: var(--accent); display: grid; place-items: center; }
.brand-text { display: flex; flex-direction: column; line-height: 1.12; }
.brand-text b { font-family: var(--serif); font-size: 1.04rem; letter-spacing: .01em; font-weight: 700; }
.brand-text span { font-size: .7rem; letter-spacing: .085em; text-transform: uppercase; color: var(--muted); margin-top: 2px; }
.topnav { display: flex; gap: 4px; margin-left: 8px; }
.topnav a {
  text-decoration: none; color: var(--ink-2); font-size: .88rem; font-weight: 550;
  padding: 8px 12px; border-radius: 8px; transition: background .15s var(--ease), color .15s;
}
.nav-short { display: none; }
.topnav a:hover { background: var(--surface-2); color: var(--ink); }
.topnav a.active { background: var(--accent-soft); color: var(--accent-ink); }
[data-theme="dark"] .topnav a.active { color: var(--accent); }
.topbar-tools { margin-left: auto; display: flex; align-items: center; gap: 3px; }
.icon-btn {
  width: 38px; height: 38px; display: grid; place-items: center; border: 0; background: transparent;
  color: var(--ink-2); border-radius: 9px; cursor: pointer; transition: background .15s, color .15s;
}
.icon-btn:hover { background: var(--surface-2); color: var(--ink); }
#theme-btn .ico-moon { display: none; }
[data-theme="dark"] #theme-btn .ico-sun { display: none; }
[data-theme="dark"] #theme-btn .ico-moon { display: block; }
.read-progress { height: 2px; background: transparent; }
.read-progress span { display: block; height: 100%; width: 0%; background: linear-gradient(90deg, var(--accent), var(--amber)); transition: width .1s linear; }

/* ---------- shared bits ---------- */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  border: 1px solid var(--ink); background: var(--ink); color: var(--bg);
  padding: 11px 19px; border-radius: 999px; font-weight: 650; font-size: .9rem;
  text-decoration: none; cursor: pointer; transition: transform .16s var(--ease), box-shadow .16s, background .16s;
}
.btn:hover { transform: translateY(-1px); box-shadow: var(--shadow-md); color: var(--bg); }
.btn:active { transform: translateY(0); }
.btn.secondary { background: var(--surface); color: var(--ink); border-color: var(--line-strong); }
.btn.secondary:hover { background: var(--surface-2); color: var(--ink); }
.btn.accent { background: var(--accent); border-color: var(--accent); color: #fff; }
.btn.accent:hover { color: #fff; }
.btn.small { padding: 7px 13px; font-size: .8rem; }
.btn.ghost { background: transparent; color: var(--ink); border-color: var(--line-strong); }
.btn.danger-ghost { background: transparent; color: var(--danger); border-color: color-mix(in srgb, var(--danger) 35%, var(--line)); }
.btn.danger-ghost:hover { background: var(--danger-soft); }

.eyebrow {
  font-size: .74rem; text-transform: uppercase; letter-spacing: .14em;
  font-weight: 700; color: var(--accent);
}
.muted { color: var(--muted); }
.small-caps { font-variant: small-caps; letter-spacing: .04em; }

/* ---------- home ---------- */
.home { max-width: 1240px; margin: 0 auto; padding: clamp(28px, 5vw, 70px) clamp(18px, 4vw, 42px) 90px; }
.home-hero {
  position: relative; display: grid; grid-template-columns: minmax(0, 1.18fr) minmax(280px, .82fr);
  gap: clamp(26px, 5vw, 70px); align-items: center; min-height: 480px;
}
.home-hero::before {
  content: ""; position: absolute; inset: -40px -60px auto -60px; height: 520px; z-index: -1;
  background-image:
    linear-gradient(color-mix(in srgb, var(--accent) 9%, transparent) 1px, transparent 1px),
    linear-gradient(90deg, color-mix(in srgb, var(--accent) 9%, transparent) 1px, transparent 1px);
  background-size: 46px 46px;
  mask-image: radial-gradient(ellipse at 35% 40%, #000 12%, transparent 72%);
  -webkit-mask-image: radial-gradient(ellipse at 35% 40%, #000 12%, transparent 72%);
  transform: perspective(700px) rotateX(54deg) translateY(-40px) scale(1.35);
  transform-origin: 50% 0;
  opacity: .8;
}
.home-hero h1 {
  font-family: var(--serif); font-size: clamp(2.4rem, 5.2vw, 4.6rem); line-height: 1.02;
  letter-spacing: -.028em; margin: .16em 0 .32em; font-weight: 700;
}
.home-hero h1 em { font-style: italic; color: var(--accent); }
.home-hero .lede { font-family: var(--serif); font-size: clamp(1.06rem, 1.6vw, 1.23rem); line-height: 1.7; color: var(--ink-2); max-width: 58ch; }
.hero-actions { display: flex; flex-wrap: wrap; gap: 11px; margin-top: 28px; }
.hero-note { margin-top: 20px; font-size: .82rem; color: var(--muted); display: flex; align-items: center; gap: 8px; }
.hero-note::before { content: ""; width: 7px; height: 7px; border-radius: 50%; background: var(--ok); box-shadow: 0 0 0 4px color-mix(in srgb, var(--ok) 15%, transparent); }

.hero-card {
  background: var(--repo-bg); color: var(--repo-ink); border: 1px solid var(--repo-line);
  border-radius: 20px; padding: clamp(22px, 3.2vw, 34px); box-shadow: var(--shadow-lg);
  position: relative; overflow: hidden;
}
.hero-card::before {
  content: ""; position: absolute; width: 280px; height: 280px; border-radius: 50%;
  right: -100px; top: -120px; border: 1px solid var(--repo-line);
  box-shadow: 0 0 0 32px rgba(77,214,255,.035), 0 0 0 66px rgba(77,214,255,.025), 0 0 0 110px rgba(77,214,255,.018);
}
.hero-card .card-label { font-size: .68rem; letter-spacing: .17em; text-transform: uppercase; color: var(--repo-accent); font-weight: 700; }
.hero-card .card-title { font-family: var(--serif); font-size: 1.45rem; line-height: 1.3; margin: 10px 0 14px; }
.hero-card p { color: var(--repo-dim); font-size: .9rem; margin: 0 0 16px; }
.hero-card .eq-mini {
  background: rgba(255,255,255,.045); border: 1px solid var(--repo-line); border-radius: 12px;
  padding: 12px 10px; color: var(--repo-ink); overflow-x: auto; font-size: .94rem;
}
.hero-card .eq-mini .katex { color: var(--repo-ink); }
.hero-card .card-foot { display: flex; justify-content: space-between; gap: 12px; align-items: center; margin-top: 18px; font-size: .74rem; color: var(--repo-dim); }
.hero-card .card-foot b { color: var(--repo-accent); font-weight: 650; }

.home-section { margin-top: clamp(56px, 8vw, 96px); }
.section-head { display: flex; align-items: flex-end; justify-content: space-between; gap: 20px; margin-bottom: 24px; }
.section-head h2 { font-family: var(--serif); font-size: clamp(1.6rem, 2.8vw, 2.25rem); margin: 0; letter-spacing: -.02em; }
.section-head p { margin: 0; color: var(--muted); font-size: .9rem; max-width: 52ch; }

.path-grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 16px; }
.path-card {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 24px; text-decoration: none; color: var(--ink); display: flex; flex-direction: column;
  min-height: 190px; transition: transform .2s var(--ease), box-shadow .2s, border-color .2s;
}
.path-card:hover { transform: translateY(-3px); box-shadow: var(--shadow-md); border-color: var(--line-strong); color: var(--ink); }
.path-card .path-num { font-family: var(--mono); font-size: .72rem; color: var(--accent); letter-spacing: .08em; }
.path-card h3 { font-family: var(--serif); font-size: 1.24rem; margin: 8px 0 8px; }
.path-card p { color: var(--muted); font-size: .86rem; line-height: 1.6; margin: 0; flex: 1; }
.path-card .path-meta { margin-top: 18px; font-size: .76rem; color: var(--ink-2); display: flex; justify-content: space-between; }

.part-map { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 14px; }
.part-card {
  display: grid; grid-template-columns: 54px minmax(0, 1fr) auto; gap: 16px; align-items: center;
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 18px 20px; text-decoration: none; color: var(--ink); transition: border-color .18s, background .18s;
}
.part-card:hover { border-color: var(--accent); background: var(--surface-2); color: var(--ink); }
.part-card .part-digit { font-family: var(--serif); font-size: 1.8rem; color: var(--accent); line-height: 1; text-align: center; }
.part-card h3 { font-family: var(--serif); font-size: 1.08rem; margin: 0 0 3px; }
.part-card p { margin: 0; color: var(--muted); font-size: .8rem; line-height: 1.5; }
.part-card .part-count { font-family: var(--mono); font-size: .72rem; color: var(--muted); white-space: nowrap; }

.destination {
  background: linear-gradient(135deg, var(--repo-bg), var(--repo-bg-2)); color: var(--repo-ink);
  border-radius: 22px; padding: clamp(26px, 4vw, 48px); display: grid; grid-template-columns: 1.05fr .95fr;
  gap: clamp(24px, 4vw, 60px); align-items: center; border: 1px solid var(--repo-line);
}
.destination h2 { font-family: var(--serif); font-size: clamp(1.6rem, 2.7vw, 2.2rem); margin: 8px 0 12px; color: #fff; }
.destination p { color: var(--repo-dim); font-size: .92rem; line-height: 1.7; margin: 0 0 12px; }
.destination .destination-eq { background: rgba(255,255,255,.05); border: 1px solid var(--repo-line); border-radius: 14px; padding: 18px 16px; overflow-x: auto; }
.destination .destination-eq .katex { color: var(--repo-ink); }
.destination .eyebrow { color: var(--repo-accent); }

.home-progress { display: flex; align-items: center; gap: 14px; margin-top: 26px; font-size: .82rem; color: var(--muted); }
.home-progress .bar { flex: 1; height: 7px; background: var(--surface-3); border-radius: 99px; overflow: hidden; max-width: 280px; }
.home-progress .bar span { display: block; height: 100%; background: linear-gradient(90deg, var(--accent), var(--amber)); border-radius: inherit; }

/* ---------- book layout ---------- */
.book-layout { display: grid; grid-template-columns: var(--sidebar-w) minmax(0, 1fr); max-width: 1520px; margin: 0 auto; }
.book-sidebar {
  position: sticky; top: var(--topbar-h); height: calc(100vh - var(--topbar-h));
  overflow-y: auto; overscroll-behavior: contain; border-right: 1px solid var(--line);
  padding: 26px 18px 46px 26px; background: color-mix(in srgb, var(--bg) 72%, var(--surface));
  scrollbar-width: thin;
}
.sidebar-head { display: flex; align-items: center; justify-content: space-between; margin-bottom: 12px; }
.sidebar-head h2 { font-size: .7rem; text-transform: uppercase; letter-spacing: .14em; color: var(--muted); margin: 0; font-weight: 700; }
.sidebar-progress { font-size: .72rem; color: var(--muted); font-family: var(--mono); }
.toc-part { margin-top: 22px; }
.toc-part:first-of-type { margin-top: 6px; }
.toc-part-head { display: flex; align-items: baseline; gap: 8px; margin-bottom: 7px; padding: 0 8px; }
.toc-part-head .digit { font-family: var(--mono); font-size: .68rem; color: var(--accent); font-weight: 700; }
.toc-part-head .name { font-size: .73rem; text-transform: uppercase; letter-spacing: .1em; color: var(--muted); font-weight: 700; }
.toc-link {
  display: flex; gap: 9px; align-items: flex-start; padding: 7px 9px; border-radius: 7px;
  text-decoration: none; color: var(--ink-2); font-size: .84rem; line-height: 1.4; position: relative;
  transition: background .13s, color .13s;
}
.toc-link:hover { background: var(--surface-2); color: var(--ink); }
.toc-link .num { font-family: var(--mono); font-size: .69rem; color: var(--muted); min-width: 25px; padding-top: 1px; }
.toc-link .mark { margin-left: auto; color: var(--ok); opacity: 0; flex: 0 0 auto; padding-top: 2px; }
.toc-link.read .mark { opacity: 1; }
.toc-link.active { background: var(--accent-soft); color: var(--accent-ink); font-weight: 650; }
[data-theme="dark"] .toc-link.active { color: var(--accent); }
.toc-link.active .num { color: var(--accent); }
.sidebar-foot { margin-top: 28px; padding: 14px 10px 0; border-top: 1px solid var(--line); font-size: .75rem; color: var(--muted); line-height: 1.55; }
.sidebar-foot a { font-weight: 600; }

.book-main { min-width: 0; padding: clamp(28px, 4.4vw, 64px) clamp(18px, 5vw, 80px) 100px; }
.chapter { max-width: 860px; margin: 0 auto; font-family: var(--serif); font-size: calc(1.075rem * var(--reading-scale)); line-height: 1.82; color: var(--ink); }
.chapter-header { margin-bottom: 34px; padding-bottom: 28px; border-bottom: 1px solid var(--line); position: relative; }
.chapter-kicker { display: flex; align-items: center; gap: 10px; font-family: var(--sans); font-size: .72rem; text-transform: uppercase; letter-spacing: .13em; color: var(--accent); font-weight: 700; }
.chapter-kicker .dot { width: 5px; height: 5px; background: var(--accent); border-radius: 50%; }
.chapter-header h1 { font-size: clamp(1.85rem, 3.8vw, 3rem); line-height: 1.12; letter-spacing: -.022em; margin: 14px 0 10px; font-weight: 700; }
.chapter-subtitle { font-size: 1.08rem; color: var(--muted); font-family: var(--sans); line-height: 1.6; margin: 0; max-width: 64ch; }
.chapter-meta { display: flex; flex-wrap: wrap; gap: 16px; margin-top: 18px; font-family: var(--sans); font-size: .76rem; color: var(--muted); align-items: center; }
.chapter-meta .sep { width: 3px; height: 3px; border-radius: 50%; background: var(--line-strong); }
.chapter-meta button { border: 0; background: transparent; color: var(--muted); padding: 0; cursor: pointer; font-size: inherit; display: inline-flex; align-items: center; gap: 5px; }
.chapter-meta button:hover { color: var(--accent); }
.chapter-meta button.done { color: var(--ok); font-weight: 650; }

.chapter p { margin: 0 0 1.05em; }
.chapter h2 { font-size: clamp(1.35rem, 2.3vw, 1.72rem); line-height: 1.25; margin: 2.1em 0 .65em; letter-spacing: -.015em; scroll-margin-top: calc(var(--topbar-h) + 20px); }
.chapter h3 { font-size: 1.15rem; line-height: 1.35; margin: 1.8em 0 .5em; letter-spacing: -.005em; scroll-margin-top: calc(var(--topbar-h) + 20px); }
.chapter h4 { font-family: var(--sans); font-size: .85rem; text-transform: uppercase; letter-spacing: .09em; color: var(--muted); margin: 1.8em 0 .55em; }
.chapter ul, .chapter ol { margin: 0 0 1.1em; padding-left: 1.35em; }
.chapter li { margin-bottom: .38em; }
.chapter strong { font-weight: 700; }
.chapter em { font-style: italic; }
.chapter hr { border: 0; border-top: 1px solid var(--line); margin: 2.2em 0; }
.chapter blockquote { margin: 1.4em 0; padding: .2em 0 .2em 1.1em; border-left: 3px solid var(--amber); color: var(--ink-2); font-style: italic; }
.chapter code { font-family: var(--mono); font-size: .84em; background: var(--surface-2); padding: .12em .35em; border-radius: 4px; border: 1px solid var(--line); }

.lead { font-size: 1.13em; line-height: 1.75; color: var(--ink-2); }
.small { font-size: .88em; color: var(--muted); }

/* boxes */
.story, .box, .exercise, .takeaway, .repo-box, .chapter-nav, .stat-strip { font-family: var(--sans); }
.story {
  background: linear-gradient(135deg, var(--amber-soft), color-mix(in srgb, var(--amber-soft) 55%, var(--surface)));
  border: 1px solid color-mix(in srgb, var(--amber) 26%, var(--line));
  border-left: 4px solid var(--amber); border-radius: 12px;
  padding: 20px 22px 16px; margin: 26px 0 30px; line-height: 1.7; font-size: calc(.96rem * var(--reading-scale));
  position: relative;
}
.story-label { display: inline-flex; align-items: center; gap: 8px; font-size: .68rem; text-transform: uppercase; letter-spacing: .13em; font-weight: 800; color: var(--amber); margin-bottom: 8px; }
.story-label .avatar { width: 21px; height: 21px; border-radius: 50%; background: var(--amber); color: #fff; display: grid; place-items: center; font-family: var(--serif); font-size: .68rem; letter-spacing: 0; }
.story p:last-child { margin-bottom: 0; }
.story em { color: var(--ink); }

.box {
  border: 1px solid var(--line); border-left-width: 4px; border-radius: 10px;
  padding: 17px 20px 13px; margin: 24px 0; background: var(--surface);
  font-size: calc(.95rem * var(--reading-scale)); line-height: 1.7;
}
.box p:last-child, .box ul:last-child, .box ol:last-child { margin-bottom: 0; }
.box-label { display: block; font-size: .66rem; text-transform: uppercase; letter-spacing: .14em; font-weight: 800; margin-bottom: 6px; color: var(--muted); }
.box.axiom { border-left-color: var(--accent); background: color-mix(in srgb, var(--accent-soft) 42%, var(--surface)); }
.box.axiom .box-label { color: var(--accent); }
.box.theorem { border-left-color: var(--indigo); background: color-mix(in srgb, var(--indigo-soft) 44%, var(--surface)); }
.box.theorem .box-label { color: var(--indigo); }
.box.definition { border-left-color: var(--line-strong); }
.box.definition .box-label { color: var(--ink-2); }
.box.warning { border-left-color: var(--amber); background: color-mix(in srgb, var(--amber-soft) 38%, var(--surface)); }
.box.warning .box-label { color: var(--amber); }
.box.check { border-left-color: var(--ok); background: color-mix(in srgb, var(--ok-soft) 38%, var(--surface)); }
.box.check .box-label { color: var(--ok); }
.box.note { border-left-color: var(--muted); background: var(--surface-2); }
.box-title { font-weight: 700; font-size: 1.01em; margin: 0 0 6px; font-family: var(--serif); }

.repo-box {
  background: linear-gradient(135deg, var(--repo-bg), var(--repo-bg-2)); color: var(--repo-ink);
  border: 1px solid var(--repo-line); border-radius: 12px; padding: 18px 20px 14px; margin: 30px 0;
  font-size: calc(.9rem * var(--reading-scale)); line-height: 1.66; position: relative; overflow: hidden;
}
.repo-box::after { content: ""; position: absolute; right: -50px; top: -60px; width: 150px; height: 150px; border: 1px solid var(--repo-line); border-radius: 50%; opacity: .55; }
.repo-box .box-label { color: var(--repo-accent); }
.repo-box a { color: var(--repo-accent); text-decoration-color: color-mix(in srgb, var(--repo-accent) 45%, transparent); }
.repo-box p:last-child { margin-bottom: 0; }
.repo-box code { background: rgba(255,255,255,.07); border-color: var(--repo-line); color: var(--repo-ink); }
.repo-box .repo-file { font-family: var(--mono); font-size: .78em; color: var(--repo-dim); }

details.proof {
  margin: 18px 0 22px; border-left: 2px dashed var(--line-strong); padding: 2px 0 2px 16px;
  font-family: var(--sans); font-size: calc(.92rem * var(--reading-scale)); line-height: 1.7;
}
details.proof summary { cursor: pointer; color: var(--accent); font-weight: 650; font-size: .87rem; list-style: none; display: flex; align-items: center; gap: 7px; }
details.proof summary::-webkit-details-marker { display: none; }
details.proof summary::before { content: "+"; font-family: var(--mono); width: 14px; color: var(--muted); }
details.proof[open] summary::before { content: "−"; }
details.proof[open] summary { margin-bottom: 10px; }
details.proof p:last-child { margin-bottom: 0; }

.eq {
  margin: 20px 0; padding: 13px 18px; background: var(--surface-2); border: 1px solid var(--line);
  border-radius: 9px; overflow-x: auto; overflow-y: hidden; font-size: .98em;
}
.eq.plain { background: transparent; border: 0; padding: 0; }
.eq .katex-display { margin: 0; }
.katex { font-size: 1.02em; }
.katex-display { overflow-x: auto; overflow-y: hidden; padding: 1px 0; }
.katex-display > .katex { white-space: normal; }
.eq-tag { float: right; font-family: var(--mono); font-size: .7rem; color: var(--muted); margin-left: 12px; padding-top: 4px; }

.table-wrap { overflow-x: auto; margin: 20px 0; border: 1px solid var(--line); border-radius: 10px; background: var(--surface); }
table.tbl { border-collapse: collapse; width: 100%; font-family: var(--sans); font-size: .84em; line-height: 1.5; min-width: 500px; }
table.tbl th, table.tbl td { padding: 9px 12px; text-align: left; border-bottom: 1px solid var(--line); vertical-align: top; }
table.tbl th { background: var(--surface-2); font-size: .76em; text-transform: uppercase; letter-spacing: .06em; color: var(--muted); font-weight: 700; white-space: nowrap; }
table.tbl tr:last-child td { border-bottom: 0; }
table.tbl td.num, table.tbl th.num { text-align: right; font-variant-numeric: tabular-nums; white-space: nowrap; }
table.tbl tr.highlight td { background: var(--amber-soft); }
table.tbl caption { caption-side: top; text-align: left; padding: 10px 12px 0; font-size: .76rem; color: var(--muted); }

.takeaway {
  margin: 34px 0 10px; padding: 20px 22px; border-top: 2px solid var(--accent); border-bottom: 2px solid var(--accent);
  font-family: var(--serif); font-size: calc(1.04rem * var(--reading-scale)); line-height: 1.7;
  color: var(--ink-2); background: color-mix(in srgb, var(--accent-soft) 22%, transparent);
}
.takeaway .box-label { color: var(--accent); font-family: var(--sans); }

.exercises { margin: 32px 0 0; }
.exercises > h3 { font-family: var(--sans); font-size: .78rem; text-transform: uppercase; letter-spacing: .13em; color: var(--muted); margin-bottom: 12px; }
.exercise { border: 1px solid var(--line); border-radius: 10px; margin-bottom: 10px; background: var(--surface); overflow: hidden; }
.exercise summary { cursor: pointer; padding: 12px 15px; font-size: .88rem; font-weight: 600; color: var(--ink-2); list-style: none; display: flex; gap: 10px; align-items: baseline; }
.exercise summary::-webkit-details-marker { display: none; }
.exercise summary::before { content: "BT"; font-family: var(--mono); font-size: .66rem; letter-spacing: .05em; color: var(--accent); border: 1px solid color-mix(in srgb, var(--accent) 35%, var(--line)); padding: 1px 5px; border-radius: 4px; flex: 0 0 auto; }
.exercise[open] summary { border-bottom: 1px solid var(--line); background: var(--surface-2); }
.exercise .answer { padding: 13px 15px 15px; font-size: .87rem; line-height: 1.7; color: var(--ink-2); background: color-mix(in srgb, var(--surface) 70%, var(--surface-2)); }
.exercise .answer p:last-child { margin-bottom: 0; }
.exercise .answer .eq { background: var(--surface); }

.chapter-nav { max-width: 860px; margin: 50px auto 0; display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }
.chapter-nav a {
  display: flex; flex-direction: column; gap: 4px; padding: 15px 17px; border: 1px solid var(--line);
  border-radius: 10px; text-decoration: none; background: var(--surface); color: var(--ink);
  transition: border-color .15s, background .15s;
}
.chapter-nav a:hover { border-color: var(--accent); background: var(--surface-2); color: var(--ink); }
.chapter-nav a.next { text-align: right; align-items: flex-end; }
.chapter-nav .dir { font-size: .68rem; text-transform: uppercase; letter-spacing: .1em; color: var(--muted); }
.chapter-nav .t { font-family: var(--serif); font-size: .95rem; line-height: 1.3; }

/* book index */
.book-index { max-width: 1000px; margin: 0 auto; padding: clamp(30px, 5vw, 64px) clamp(18px, 4vw, 40px) 90px; }
.book-index h1 { font-family: var(--serif); font-size: clamp(2rem, 4vw, 3.2rem); letter-spacing: -.025em; margin: 12px 0 14px; }
.book-index .lede { max-width: 65ch; color: var(--ink-2); font-family: var(--serif); font-size: 1.1rem; line-height: 1.7; }
.index-part { margin-top: 40px; }
.index-part-head { display: flex; align-items: baseline; gap: 14px; padding-bottom: 10px; border-bottom: 1px solid var(--line); margin-bottom: 10px; }
.index-part-head .digit { font-family: var(--mono); color: var(--accent); font-size: .8rem; }
.index-part-head h2 { font-family: var(--serif); font-size: 1.35rem; margin: 0; }
.index-part-head p { margin: 0 0 0 auto; color: var(--muted); font-size: .8rem; }
.index-chapter { display: flex; gap: 14px; align-items: baseline; padding: 10px 4px; border-bottom: 1px dotted var(--line); text-decoration: none; color: var(--ink-2); }
.index-chapter:hover { color: var(--accent-ink); }
.index-chapter .num { font-family: var(--mono); font-size: .72rem; color: var(--muted); min-width: 32px; }
.index-chapter .t { font-family: var(--serif); font-size: 1rem; }
.index-chapter .mins { margin-left: auto; font-size: .72rem; color: var(--muted); white-space: nowrap; }
.index-chapter .read-dot { width: 6px; height: 6px; border-radius: 50%; background: var(--ok); opacity: 0; }
.index-chapter.read .read-dot { opacity: 1; }

/* ---------- lab ---------- */
.lab-layout { display: grid; grid-template-columns: 272px minmax(0, 1fr); max-width: 1600px; margin: 0 auto; min-height: calc(100vh - var(--topbar-h)); }
.lab-sidebar {
  position: sticky; top: var(--topbar-h); height: calc(100vh - var(--topbar-h)); overflow-y: auto;
  border-right: 1px solid var(--line); padding: 22px 14px 40px 20px; background: color-mix(in srgb, var(--bg) 72%, var(--surface));
  scrollbar-width: thin;
}
.lab-sidebar h2 { font-size: .7rem; text-transform: uppercase; letter-spacing: .14em; color: var(--muted); margin: 0 0 12px 8px; }
.lab-group { margin-top: 15px; }
.lab-group-head { font-size: .64rem; text-transform: uppercase; letter-spacing: .12em; color: var(--accent); font-weight: 800; padding: 0 8px; margin-bottom: 5px; }
.lab-step-link { display: flex; gap: 9px; padding: 6px 8px; border-radius: 6px; text-decoration: none; color: var(--ink-2); font-size: .8rem; line-height: 1.35; align-items: baseline; }
.lab-step-link:hover { background: var(--surface-2); color: var(--ink); }
.lab-step-link.active { background: var(--accent-soft); color: var(--accent-ink); font-weight: 650; }
[data-theme="dark"] .lab-step-link.active { color: var(--accent); }
.lab-step-link .n { font-family: var(--mono); font-size: .66rem; color: var(--muted); min-width: 20px; }
.lab-step-link.active .n { color: var(--accent); }
.lab-step-link .seen { margin-left: auto; color: var(--ok); opacity: 0; }
.lab-step-link.seen .seen { opacity: 1; }
.lab-sidebar .side-note { margin-top: 26px; border-top: 1px solid var(--line); padding: 14px 8px 0; font-size: .73rem; color: var(--muted); line-height: 1.55; }

.lab-main { min-width: 0; padding: 22px clamp(14px, 2.6vw, 34px) 60px; }
.lab-top { display: flex; align-items: flex-start; gap: 18px; justify-content: space-between; margin-bottom: 14px; }
.lab-top .eyebrow { margin-bottom: 4px; }
.lab-top h1 { font-family: var(--serif); font-size: clamp(1.4rem, 2.5vw, 2.05rem); line-height: 1.2; letter-spacing: -.018em; margin: 0; }
.lab-nav-btns { display: flex; gap: 7px; flex: 0 0 auto; padding-top: 4px; }
.lab-nav-btns button { border: 1px solid var(--line-strong); background: var(--surface); color: var(--ink-2); border-radius: 8px; width: 36px; height: 36px; display: grid; place-items: center; cursor: pointer; }
.lab-nav-btns button:hover:not(:disabled) { border-color: var(--accent); color: var(--accent); }
.lab-nav-btns button:disabled { opacity: .35; cursor: default; }
.lab-nav-btns .lab-sidebar-toggle { display: none; }

.lab-stage { background: var(--lab-bg); border: 1px solid var(--line); border-radius: 16px; overflow: hidden; box-shadow: var(--shadow-sm); }
.canvas-wrap { position: relative; width: 100%; aspect-ratio: 1000 / 620; background: var(--lab-bg); }
.canvas-wrap canvas { width: 100%; height: 100%; display: block; }
.canvas-hud { position: absolute; top: 14px; left: 16px; right: 16px; display: flex; justify-content: space-between; align-items: flex-start; gap: 12px; pointer-events: none; }
.hud-chip { font-family: var(--mono); font-size: .66rem; letter-spacing: .06em; color: var(--lab-dim); background: color-mix(in srgb, var(--lab-bg) 76%, transparent); border: 1px solid color-mix(in srgb, var(--lab-ink) 16%, transparent); padding: 5px 8px; border-radius: 5px; backdrop-filter: blur(8px); }
.hud-chip b { color: var(--lab-ink); font-weight: 600; }
.canvas-caption { padding: 8px 16px; font-family: var(--sans); font-size: .7rem; color: var(--lab-dim); border-top: 1px solid var(--lab-line); background: var(--lab-bg-2); display: flex; justify-content: space-between; gap: 14px; flex-wrap: wrap; }
.canvas-caption .legend { display: flex; gap: 12px; flex-wrap: wrap; }
.legend-item { display: inline-flex; align-items: center; gap: 5px; }
.legend-swatch { width: 8px; height: 8px; border-radius: 2px; display: inline-block; }

.lab-playbar { display: flex; align-items: center; gap: 10px; padding: 9px 12px; border-top: 1px solid var(--lab-line); background: var(--lab-bg-2); color: var(--lab-dim); font-size: .72rem; }
.lab-playbar button { border: 1px solid var(--lab-line); background: var(--lab-bg); color: var(--lab-ink); border-radius: 6px; padding: 5px 11px; cursor: pointer; font-size: .72rem; }
.lab-playbar button:hover { border-color: var(--lab-cyan); color: var(--lab-cyan); }
.lab-playbar .time { font-family: var(--mono); margin-left: auto; }

.lab-grid { display: grid; grid-template-columns: minmax(0, 1.08fr) minmax(300px, .92fr); gap: 16px; margin-top: 16px; align-items: start; }
.lab-panel { background: var(--surface); border: 1px solid var(--line); border-radius: 13px; padding: 20px 21px; }
.lab-panel h2 { font-family: var(--serif); font-size: 1.16rem; margin: 0 0 8px; }
.lab-panel .intro { font-family: var(--serif); font-size: .96rem; line-height: 1.72; color: var(--ink-2); }
.lab-panel .intro p { margin: 0 0 .8em; }
.lab-panel .intro p:last-child { margin-bottom: 0; }
.lab-formula { background: var(--surface-2); border: 1px solid var(--line); border-radius: 8px; padding: 10px 13px; margin: 13px 0; overflow-x: auto; }
.lab-formula .katex { font-size: .95em; }
.lab-note { font-size: .8rem; line-height: 1.6; color: var(--muted); border-left: 2px solid var(--amber); padding-left: 11px; margin-top: 12px; }
.lab-note b { color: var(--ink-2); }
.lab-question { font-size: .8rem; line-height: 1.55; color: var(--ink-2); background: var(--accent-soft); border-radius: 8px; padding: 9px 11px; margin-top: 12px; }
.lab-question b { color: var(--accent-ink); }
[data-theme="dark"] .lab-question b { color: var(--accent); }

.lab-controls { background: var(--surface); border: 1px solid var(--line); border-radius: 13px; padding: 16px 18px; }
.lab-controls h2 { font-family: var(--sans); font-size: .7rem; text-transform: uppercase; letter-spacing: .13em; color: var(--muted); margin: 0 0 12px; }
.control-row { margin-bottom: 14px; }
.control-row:last-child { margin-bottom: 0; }
.control-label { display: flex; justify-content: space-between; gap: 12px; font-size: .78rem; color: var(--ink-2); margin-bottom: 5px; }
.control-label output { font-family: var(--mono); font-size: .72rem; color: var(--accent); font-weight: 600; }
input[type="range"] { width: 100%; accent-color: var(--accent); height: 22px; cursor: pointer; }
input[type="range"]:disabled { opacity: .5; cursor: default; }
select.control-select { width: 100%; border: 1px solid var(--line-strong); background: var(--surface); color: var(--ink); border-radius: 7px; padding: 7px 9px; font-size: .8rem; }
.toggle-row { display: flex; align-items: center; justify-content: space-between; gap: 12px; padding: 7px 0; }
.toggle-row .t-label { font-size: .79rem; color: var(--ink-2); line-height: 1.35; }
.switch { display: inline-flex; width: 38px; height: 22px; flex: 0 0 auto; position: relative; cursor: pointer; }
.switch input { position: absolute; opacity: 0; width: 100%; height: 100%; margin: 0; cursor: pointer; }
.switch span { position: absolute; inset: 0; background: var(--surface-3); border: 1px solid var(--line-strong); border-radius: 99px; transition: background .16s, border-color .16s; }
.switch span::after { content: ""; position: absolute; width: 16px; height: 16px; left: 2px; top: 2px; background: var(--surface); border-radius: 50%; box-shadow: 0 1px 2px rgba(0,0,0,.2); transition: transform .16s var(--ease); }
.switch input:checked + span { background: var(--accent); border-color: var(--accent); }
.switch input:checked + span::after { transform: translateX(16px); background: #fff; }
.switch input:focus-visible + span { outline: 2px solid var(--amber); outline-offset: 2px; }

.readout-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(100px, 1fr)); gap: 8px; margin-top: 12px; }
.readout { background: var(--surface-2); border: 1px solid var(--line); border-radius: 7px; padding: 7px 9px; }
.readout .k { display: block; font-size: .64rem; text-transform: uppercase; letter-spacing: .07em; color: var(--muted); margin-bottom: 1px; }
.readout .v { font-family: var(--mono); font-size: .8rem; color: var(--ink); font-weight: 600; }

.lab-keys { margin-top: 14px; font-size: .72rem; color: var(--muted); display: flex; flex-wrap: wrap; gap: 12px; }

/* ---------- dialogs ---------- */
dialog { border: 0; padding: 0; color: var(--ink); background: var(--surface); border-radius: 16px; box-shadow: var(--shadow-lg); }
dialog::backdrop { background: rgba(8, 14, 24, .55); backdrop-filter: blur(4px); }
.search-dialog { width: min(680px, calc(100vw - 28px)); max-height: min(76vh, 720px); margin: 10vh auto auto; overflow: hidden; }
.search-head { display: flex; align-items: center; justify-content: space-between; padding: 17px 20px 0; }
.search-head h2 { font-family: var(--serif); font-size: 1.2rem; margin: 0; }
.search-field { display: block; padding: 13px 20px 0; }
.search-field input { width: 100%; border: 1px solid var(--line-strong); background: var(--surface-2); color: var(--ink); border-radius: 9px; padding: 11px 13px; font-size: .95rem; font-family: var(--sans); }
.search-field input:focus { outline: 2px solid var(--accent); outline-offset: 1px; }
.search-hint { padding: 8px 20px 0; margin: 0; font-size: .72rem; color: var(--muted); }
.search-results { overflow-y: auto; max-height: 50vh; padding: 10px 10px 14px; }
.search-result { display: block; width: 100%; text-align: left; border: 0; background: transparent; padding: 10px 11px; border-radius: 8px; cursor: pointer; color: var(--ink); }
.search-result:hover, .search-result.active { background: var(--surface-2); }
.search-result .sr-top { display: flex; gap: 8px; align-items: baseline; font-size: .72rem; color: var(--accent); margin-bottom: 2px; }
.search-result .sr-title { font-family: var(--serif); font-size: .96rem; font-weight: 650; margin-bottom: 2px; }
.search-result .sr-snip { font-size: .76rem; color: var(--muted); line-height: 1.5; display: -webkit-box; -webkit-line-clamp: 2; -webkit-box-orient: vertical; overflow: hidden; }
.search-empty { padding: 24px 14px; text-align: center; color: var(--muted); font-size: .85rem; }

.settings-dialog { width: min(600px, calc(100vw - 28px)); max-height: 84vh; margin: 8vh auto auto; overflow-y: auto; }
.settings-grid { padding: 6px 20px 22px; }
.setting-row { display: flex; align-items: center; justify-content: space-between; gap: 18px; padding: 14px 0; border-bottom: 1px solid var(--line); }
.setting-row b { font-size: .88rem; }
.setting-row p { margin: 2px 0 0; font-size: .75rem; color: var(--muted); line-height: 1.45; }
.setting-block { padding: 16px 0 0; }
.setting-block b { font-size: .88rem; }
.setting-block p { font-size: .76rem; color: var(--muted); line-height: 1.55; margin: 4px 0 10px; }
.settings-actions { display: flex; gap: 8px; flex-wrap: wrap; }
.segmented { display: inline-flex; border: 1px solid var(--line-strong); border-radius: 8px; overflow: hidden; flex: 0 0 auto; }
.segmented button { border: 0; background: var(--surface); color: var(--muted); padding: 6px 10px; font-size: .74rem; cursor: pointer; border-right: 1px solid var(--line); }
.segmented button:last-child { border-right: 0; }
.segmented button.active { background: var(--accent); color: #fff; }
.segmented button:hover:not(.active) { background: var(--surface-2); color: var(--ink); }

/* ---------- footer ---------- */
.site-footer { border-top: 1px solid var(--line); background: color-mix(in srgb, var(--bg) 80%, var(--surface)); }
.footer-inner { max-width: 1000px; margin: 0 auto; padding: 34px clamp(18px, 4vw, 40px); font-size: .78rem; color: var(--muted); line-height: 1.65; }
.footer-inner p { max-width: 78ch; margin: 0 0 8px; }
.footer-meta { font-size: .72rem; }

/* mobile */
.sidebar-toggle, .lab-sidebar-toggle { display: none; }
.sidebar-backdrop {
  position: fixed; inset: var(--topbar-h) 0 0; z-index: 54; background: rgba(8,14,24,.48);
  opacity: 0; pointer-events: none; transition: opacity .22s var(--ease); backdrop-filter: blur(2px);
}
.sidebar-backdrop.show { opacity: 1; pointer-events: auto; }
body[data-view="lab"] .site-footer { display: none; }
body[data-view="lab"] .read-progress { opacity: .45; }
@media (max-width: 1100px) {
  .home-hero { grid-template-columns: 1fr; min-height: 0; }
  .hero-card { max-width: 560px; }
  .lab-grid { grid-template-columns: 1fr; }
  .lab-controls { order: 2; }
  .lab-panel { order: 1; }
}
@media (max-width: 980px) {
  .book-layout { grid-template-columns: 1fr; }
  .book-sidebar {
    position: fixed; left: 0; top: var(--topbar-h); z-index: 55; width: min(330px, 86vw);
    height: calc(100vh - var(--topbar-h)); transform: translateX(-102%); transition: transform .22s var(--ease);
    background: var(--surface); box-shadow: var(--shadow-lg); border-right: 1px solid var(--line);
  }
  .book-sidebar.open { transform: translateX(0); }
  .sidebar-toggle { display: inline-flex; }
  .book-main { padding-top: 24px; }
  .chapter { max-width: 100%; }
  .lab-layout { grid-template-columns: 1fr; }
  .lab-sidebar {
    position: fixed; left: 0; top: var(--topbar-h); z-index: 55; width: min(320px, 86vw);
    height: calc(100vh - var(--topbar-h)); transform: translateX(-102%); transition: transform .22s var(--ease);
    background: var(--surface); box-shadow: var(--shadow-lg);
  }
  .lab-sidebar.open { transform: translateX(0); }
  .lab-nav-btns .lab-sidebar-toggle { display: inline-flex; width: auto; padding: 0 10px; white-space: nowrap; }
  .lab-main { padding-top: 14px; }
}
@media (max-width: 760px) {
  :root { --topbar-h: 58px; }
  .topbar-inner { gap: 8px; padding: 0 10px; }
  .brand-text span { display: none; }
  .brand-text b { font-size: .95rem; }
  .topnav { margin-left: 2px; gap: 0; }
  .topnav a { padding: 7px 6px; font-size: .78rem; white-space: nowrap; }
  .topnav a[data-nav="toc"] { display: none; }
  .nav-full { display: none; }
  .nav-short { display: inline; }
  .topbar-tools { gap: 0; }
  .icon-btn { width: 34px; height: 34px; }
  .home { padding-top: 24px; }
  .home-hero h1 { font-size: clamp(2.15rem, 10vw, 3.1rem); }
  .path-grid { grid-template-columns: 1fr; }
  .part-map { grid-template-columns: 1fr; }
  .destination { grid-template-columns: 1fr; }
  .section-head { flex-direction: column; align-items: flex-start; gap: 6px; }
  .chapter { font-size: calc(1.03rem * var(--reading-scale)); }
  .chapter-header h1 { font-size: clamp(1.7rem, 6.4vw, 2.3rem); }
  .chapter-kicker { flex-wrap: wrap; row-gap: 5px; }
  .chapter-kicker .dot { display: none; }
  .chapter-kicker span:last-child { white-space: nowrap; }
  .chapter-meta { gap: 10px 14px; }
  .chapter-meta .sep { display: none; }
  .chapter-nav { grid-template-columns: 1fr; }
  .chapter-nav a.next { text-align: left; align-items: flex-start; }
  .story, .box, .repo-box { padding-left: 15px; padding-right: 15px; }
  .eq { padding: 10px; }
  .canvas-wrap { aspect-ratio: 1000 / 700; }
  .canvas-hud { top: 9px; left: 9px; right: 9px; }
  .hud-chip { font-size: .58rem; padding: 4px 6px; }
  .canvas-caption { padding: 7px 9px; font-size: .62rem; gap: 6px; }
  .lab-top { flex-wrap: wrap; }
  .lab-panel { padding: 16px; }
  .lab-controls { padding: 14px; }
  .setting-row { flex-direction: column; align-items: flex-start; gap: 8px; }
  .search-dialog { margin-top: 6vh; }
}
@media (min-width: 981px) {
  .sidebar-backdrop { display: none; }
}
@media print {
  .topbar, .book-sidebar, .site-footer, .chapter-nav, .chapter-meta button, .skip-link, .sidebar-toggle { display: none !important; }
  .book-layout { display: block; }
  .book-main, .chapter { max-width: 100%; padding: 0; }
  body { background: #fff; color: #000; }
  .story, .box, .repo-box, .eq { break-inside: avoid; }
  a { color: #000; text-decoration: underline; }
}