/* Data Town — shared design system for every chapter page.
   Tokens first (light), then dark overrides, then components. */

:root {
  --bg: #EAEFF5;
  --bg-dot: rgba(48, 86, 240, 0.10);
  --surface: #FFFFFF;
  --surface-2: #F4F7FB;
  --line: #D3DBE6;
  --line-strong: #AEB9CA;
  --ink: #131A2B;
  --ink-2: #465066;
  --ink-3: #768099;

  --blue: #2F55EE;
  --blue-soft: #DCE4FF;
  --sun: #F5A300;
  --sun-soft: #FFEFC7;
  --coral: #E8503F;
  --coral-soft: #FDE0DB;
  --mint: #0E9E7B;
  --mint-soft: #D1F2E8;
  --lilac: #7656E6;
  --lilac-soft: #E7E0FF;

  --on-accent: #FFFFFF;
  --shadow: 0 1px 0 rgba(19, 26, 43, 0.05), 0 10px 28px -16px rgba(19, 26, 43, 0.25);
  --r-s: 8px;
  --r-m: 14px;
  --r-l: 22px;

  --f-display: "Bricolage Grotesque", "Avenir Next", "Segoe UI", system-ui, sans-serif;
  --f-body: "Atkinson Hyperlegible", "Segoe UI", system-ui, -apple-system, sans-serif;
  --f-mono: "JetBrains Mono", ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  color-scheme: light;
}

:root[data-theme="dark"] {
  --bg: #0D1220;
  --bg-dot: rgba(120, 146, 255, 0.10);
  --surface: #151C2D;
  --surface-2: #1A2336;
  --line: #28324A;
  --line-strong: #3D4A68;
  --ink: #EAF0FA;
  --ink-2: #B2BCD1;
  --ink-3: #7F8AA4;
  --blue: #7390FF;
  --blue-soft: #1E2A58;
  --sun: #FFC247;
  --sun-soft: #3B3014;
  --coral: #FF7B6B;
  --coral-soft: #44211E;
  --mint: #3DD3AA;
  --mint-soft: #0F3B31;
  --lilac: #A68EFF;
  --lilac-soft: #2A2253;
  --on-accent: #0D1220;
  --shadow: 0 1px 0 rgba(0, 0, 0, 0.3), 0 14px 32px -18px rgba(0, 0, 0, 0.7);
  color-scheme: dark;
}

/* ---------- base ---------- */
html { scroll-behavior: smooth; }
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }
body {
  background: var(--bg);
  color: var(--ink);
  font-family: var(--f-body);
  font-size: 17px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}
h1, h2, h3, h4 { font-family: var(--f-display); line-height: 1.08; margin: 0; text-wrap: balance; letter-spacing: -0.02em; }
p { margin: 0; }
a { color: var(--blue); }
:focus-visible { outline: 3px solid var(--blue); outline-offset: 2px; border-radius: 4px; }
code, .mono { font-family: var(--f-mono); font-size: 0.88em; }
b, strong { font-weight: 700; }

.wrap { max-width: 1160px; margin: 0 auto; padding-inline: 20px; }

/* ---------- top bar ---------- */
.topbar {
  position: sticky; top: env(safe-area-inset-top, 0px); z-index: 50;
  background: color-mix(in srgb, var(--bg) 86%, transparent);
  backdrop-filter: blur(10px); -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line);
}
.topbar .wrap { display: flex; align-items: center; gap: 14px; min-height: 58px; }
.brand { display: inline-flex; align-items: center; gap: 10px; font-family: var(--f-display); font-weight: 700; font-size: 18px; color: var(--ink); text-decoration: none; letter-spacing: -0.01em; }
.brand-mark { width: 26px; height: 26px; flex: none; }
.topbar .where { color: var(--ink-3); font-size: 14px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; min-width: 0; }
.topbar .spacer { flex: 1; }
.dots { display: flex; gap: 4px; }
.dots a { width: 9px; height: 9px; border-radius: 3px; background: var(--line); display: block; }
.dots a.done { background: var(--mint); }
.dots .soon { width: 9px; height: 9px; border-radius: 3px; background: var(--line); opacity: .4; display: block; }
.dots a.here { background: var(--blue); transform: scale(1.25); }
.navbtn { display: inline-flex; align-items: center; justify-content: center; width: 36px; height: 36px; border-radius: 10px; border: 1px solid var(--line); color: var(--ink); text-decoration: none; background: var(--surface); font-size: 18px; }
.navbtn.wide { width: auto; padding-inline: 12px; font-size: 13px; font-weight: 700; font-family: var(--f-body); }
.navbtn[aria-disabled="true"] { opacity: .35; pointer-events: none; }
.theme-switch { display: inline-flex; flex: none; background: var(--surface); border: 1px solid var(--line); border-radius: 10px; padding: 2px; gap: 2px; }
.theme-switch button { appearance: none; border: 0; background: transparent; color: var(--ink-2); width: 32px; height: 32px; padding: 0; border-radius: 8px; cursor: pointer; display: inline-grid; place-items: center; }
.theme-switch svg { width: 18px; height: 18px; display: block; }
.theme-switch .theme-ico { fill: none; stroke: currentColor; stroke-width: 2; stroke-linecap: round; }
.theme-switch .theme-moon { fill: currentColor; }
.theme-switch button[aria-pressed="true"] { background: var(--ink); color: var(--bg); }
@media (max-width: 760px) {
  .dots { display: none; }
  .topbar .where { font-size: 13px; }
  .topbar .wrap { gap: 8px; }
}

/* ---------- chapter hero ---------- */
.hero { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1.05fr); gap: 40px; align-items: center; padding-block: 48px 36px; }
.ch-tag { display: inline-flex; align-items: center; gap: 10px; font-family: var(--f-mono); font-size: 13px; letter-spacing: .08em; text-transform: uppercase; color: var(--ink-2); }
.ch-tag .num { display: inline-grid; place-items: center; min-width: 40px; height: 40px; padding-inline: 8px; border-radius: 12px; background: var(--ink); color: var(--bg); font-family: var(--f-display); font-size: 20px; font-weight: 800; letter-spacing: 0; }
.hero h1 { font-size: clamp(38px, 5.6vw, 66px); font-weight: 800; margin-top: 18px; }
.hero .lede { font-size: clamp(18px, 2vw, 21px); color: var(--ink-2); margin-top: 18px; max-width: 34ch; }
.hero .quote { margin-top: 22px; padding-left: 14px; border-left: 3px solid var(--sun); color: var(--ink-3); font-size: 15px; max-width: 46ch; }
.hero-stage { aspect-ratio: 5 / 4; max-width: 100%; }
.toc { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 26px; }
.toc a { font-size: 14px; text-decoration: none; color: var(--ink); background: var(--surface); border: 1px solid var(--line); padding: 6px 12px; border-radius: 999px; }
.toc a:hover { border-color: var(--blue); color: var(--blue); }
@media (max-width: 900px) { .hero { grid-template-columns: 1fr; gap: 26px; padding-block: 30px 18px; } }

/* ---------- scenes ---------- */
.scene { padding-block: 56px; border-top: 1px dashed var(--line-strong); scroll-margin-top: 70px; }
.scene-grid { display: grid; grid-template-columns: minmax(0, 0.8fr) minmax(0, 1.2fr); gap: 40px; align-items: start; }
.scene-grid.flip { grid-template-columns: minmax(0, 1.2fr) minmax(0, 0.8fr); }
.scene-grid.flip > .copy { order: 2; }
.scene-grid.full { grid-template-columns: 1fr; }
@media (max-width: 900px) {
  .scene { padding-block: 40px; }
  .scene-grid, .scene-grid.flip { grid-template-columns: 1fr; gap: 22px; }
  .scene-grid.flip > .copy { order: 0; }
}
.copy { display: flex; flex-direction: column; gap: 14px; }
.eyebrow { font-family: var(--f-mono); font-size: 12.5px; letter-spacing: .1em; text-transform: uppercase; color: var(--blue); }
.scene h2 { font-size: clamp(28px, 3.4vw, 40px); font-weight: 750; }
.story { font-size: 18px; color: var(--ink); max-width: 60ch; }
.story + .story { margin-top: -2px; }
.imagine { background: var(--sun-soft); border-radius: var(--r-m); padding: 14px 16px; font-size: 16.5px; color: var(--ink); }
.imagine b { font-family: var(--f-display); }

/* grown-up box: the book's precise terms */
details.book { border: 1px solid var(--line); border-radius: var(--r-m); background: var(--surface); }
details.book summary { cursor: pointer; list-style: none; padding: 12px 16px; font-weight: 700; font-size: 15px; display: flex; align-items: center; gap: 10px; color: var(--ink-2); }
details.book summary::-webkit-details-marker { display: none; }
details.book summary::before { content: "+"; display: inline-grid; place-items: center; width: 22px; height: 22px; border-radius: 6px; background: var(--surface-2); border: 1px solid var(--line); font-family: var(--f-mono); color: var(--ink); }
details.book[open] summary::before { content: "–"; }
details.book .inner { padding: 0 16px 16px; font-size: 15.5px; color: var(--ink-2); display: flex; flex-direction: column; gap: 10px; }
details.book ul { margin: 0; padding-left: 18px; display: flex; flex-direction: column; gap: 6px; }
details.book .cite {
  margin-top: 4px;
  padding-top: 10px;
  border-top: 1px dashed var(--line);
  font-family: var(--f-mono);
  font-size: 12px;
  line-height: 1.45;
  color: var(--ink-3);
}
details.book .cite i { font-family: var(--f-display); font-style: italic; font-weight: 600; color: var(--ink-2); }
.cite-note { font-size: 14.5px; color: var(--ink-3); max-width: 62ch; }
.cite-note i { font-style: italic; }

/* ---------- the stage (simulation panel) ---------- */
.stage {
  position: relative;
  background-color: var(--surface);
  background-image: radial-gradient(var(--bg-dot) 1.2px, transparent 1.3px);
  background-size: 18px 18px;
  border: 1px solid var(--line);
  border-radius: var(--r-l);
  box-shadow: var(--shadow);
  overflow: hidden;
}
.stage svg { display: block; width: 100%; height: auto; }
.stage-scroll { overflow-x: auto; }
.stage-scroll > svg { min-width: 560px; }
.stage-head { display: flex; align-items: center; justify-content: space-between; gap: 10px; flex-wrap: wrap; padding: 12px 14px; border-bottom: 1px solid var(--line); background: color-mix(in srgb, var(--surface) 92%, transparent); }
.stage-title { font-family: var(--f-mono); font-size: 12px; letter-spacing: .08em; text-transform: uppercase; color: var(--ink-3); }
.controls { display: flex; flex-wrap: wrap; align-items: center; gap: 10px; padding: 12px 14px; border-top: 1px solid var(--line); background: var(--surface-2); }
.controls .grow { flex: 1; }
.caption { padding: 12px 16px; border-top: 1px solid var(--line); font-size: 15px; color: var(--ink-2); min-height: 48px; background: var(--surface); }
.caption b { color: var(--ink); }

/* buttons */
.btn {
  appearance: none; border: 1px solid var(--line-strong); background: var(--surface); color: var(--ink);
  font: 700 14.5px/1 var(--f-body); padding: 10px 14px; border-radius: 11px; cursor: pointer;
  display: inline-flex; align-items: center; gap: 8px; transition: transform .12s, background .15s, border-color .15s;
}
.btn:hover { border-color: var(--ink-3); }
.btn:active { transform: translateY(1px); }
.btn:disabled { opacity: .45; cursor: not-allowed; }
.btn.primary { background: var(--blue); border-color: var(--blue); color: var(--on-accent); }
.btn.danger { background: var(--coral-soft); border-color: var(--coral); color: var(--ink); }
.btn.good { background: var(--mint-soft); border-color: var(--mint); color: var(--ink); }
.btn.small { padding: 7px 10px; font-size: 13px; border-radius: 9px; }

/* segmented control */
.seg { display: inline-flex; background: var(--surface); border: 1px solid var(--line-strong); border-radius: 12px; padding: 3px; gap: 2px; flex-wrap: wrap; }
.seg button { appearance: none; border: 0; background: transparent; color: var(--ink-2); font: 700 14px/1 var(--f-body); padding: 8px 12px; border-radius: 9px; cursor: pointer; }
.seg button[aria-pressed="true"] { background: var(--ink); color: var(--bg); }

/* slider */
.slider { display: flex; align-items: center; gap: 10px; font-size: 14px; color: var(--ink-2); flex-wrap: wrap; }
.slider label { font-weight: 700; color: var(--ink); }
.slider output { font-family: var(--f-mono); font-variant-numeric: tabular-nums; color: var(--ink); min-width: 4ch; }
input[type="range"] { accent-color: var(--blue); width: 160px; max-width: 100%; }

/* stats */
.stats { display: flex; flex-wrap: wrap; gap: 8px; }
.stat { display: inline-flex; flex-direction: column; gap: 2px; padding: 8px 12px; border-radius: 12px; background: var(--surface-2); border: 1px solid var(--line); min-width: 96px; }
.stat .k { font-size: 11.5px; letter-spacing: .06em; text-transform: uppercase; color: var(--ink-3); font-family: var(--f-mono); }
.stat .v { font-family: var(--f-mono); font-size: 18px; font-weight: 700; font-variant-numeric: tabular-nums; color: var(--ink); }
.stat.good .v { color: var(--mint); }
.stat.bad .v { color: var(--coral); }
.stat.warn .v { color: var(--sun); }

.pill { display: inline-flex; align-items: center; gap: 6px; font-size: 12.5px; font-weight: 700; padding: 3px 9px; border-radius: 999px; background: var(--surface-2); border: 1px solid var(--line); color: var(--ink-2); }
.pill.good { background: var(--mint-soft); border-color: transparent; color: var(--ink); }
.pill.bad { background: var(--coral-soft); border-color: transparent; color: var(--ink); }
.pill.warn { background: var(--sun-soft); border-color: transparent; color: var(--ink); }
.pill.info { background: var(--blue-soft); border-color: transparent; color: var(--ink); }
.pill i { width: 8px; height: 8px; border-radius: 50%; background: currentColor; display: inline-block; }
.pill.good i { background: var(--mint); } .pill.bad i { background: var(--coral); } .pill.warn i { background: var(--sun); } .pill.info i { background: var(--blue); }

/* ---------- SVG vocabulary (use these classes inside sims) ---------- */
.sv-text { fill: var(--ink); font-family: var(--f-body); font-size: 14px; }
.sv-label { fill: var(--ink-2); font-family: var(--f-mono); font-size: 11px; letter-spacing: .02em; }
.sv-title { fill: var(--ink); font-family: var(--f-display); font-size: 17px; font-weight: 700; }
.sv-big { fill: var(--ink); font-family: var(--f-display); font-size: 26px; font-weight: 800; }
.sv-muted { fill: var(--ink-3); }
.sv-box { fill: var(--surface); stroke: var(--line-strong); stroke-width: 1.5; }
.sv-panel { fill: var(--surface-2); stroke: var(--line); stroke-width: 1; }
.sv-server { fill: var(--blue-soft); stroke: var(--blue); stroke-width: 2; }
.sv-db { fill: var(--lilac-soft); stroke: var(--lilac); stroke-width: 2; }
.sv-data { fill: var(--sun); stroke: none; }
.sv-data-soft { fill: var(--sun-soft); stroke: var(--sun); stroke-width: 1.5; }
.sv-good { fill: var(--mint-soft); stroke: var(--mint); stroke-width: 2; }
.sv-bad { fill: var(--coral-soft); stroke: var(--coral); stroke-width: 2; }
.sv-fill-blue { fill: var(--blue); } .sv-fill-sun { fill: var(--sun); } .sv-fill-coral { fill: var(--coral); }
.sv-fill-mint { fill: var(--mint); } .sv-fill-lilac { fill: var(--lilac); } .sv-fill-ink { fill: var(--ink); }
.sv-fill-line { fill: var(--line); } .sv-fill-surface { fill: var(--surface); }
.sv-wire { fill: none; stroke: var(--line-strong); stroke-width: 2; stroke-dasharray: 5 6; }
.sv-wire-solid { fill: none; stroke: var(--line-strong); stroke-width: 2; }
.sv-wire-live { fill: none; stroke: var(--blue); stroke-width: 2.5; stroke-dasharray: 6 6; animation: dash 0.9s linear infinite; }
@keyframes dash { to { stroke-dashoffset: -24; } }
.sv-pop { animation: pop .45s cubic-bezier(.2,1.6,.4,1); transform-box: fill-box; transform-origin: center; }
@keyframes pop { from { transform: scale(.4); opacity: 0; } to { transform: scale(1); opacity: 1; } }
.sv-shake { animation: shake .4s; transform-box: fill-box; transform-origin: center; }
@keyframes shake { 20% { transform: translateX(-4px); } 40% { transform: translateX(4px); } 60% { transform: translateX(-3px); } 80% { transform: translateX(3px); } }
.sv-pulse { animation: pulse 1.6s ease-in-out infinite; transform-box: fill-box; transform-origin: center; }
@keyframes pulse { 50% { transform: scale(1.06); } }
@media (prefers-reduced-motion: reduce) { .sv-wire-live, .sv-pulse { animation: none; } .sv-pop, .sv-shake { animation-duration: .01s; } }

/* ---------- cards used by summaries ---------- */
.cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 14px; }
.card { background: var(--surface); border: 1px solid var(--line); border-radius: var(--r-m); padding: 16px; display: flex; flex-direction: column; gap: 8px; }
.card h3 { font-size: 19px; font-weight: 700; }
.card p { font-size: 15.5px; color: var(--ink-2); }

/* trade-off seesaw rows */
.tradeoffs { display: flex; flex-direction: column; gap: 12px; }
.tradeoff { display: grid; grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr); align-items: center; gap: 14px; background: var(--surface); border: 1px solid var(--line); border-radius: var(--r-m); padding: 14px 16px; }
.tradeoff .side h4 { font-size: 17px; }
.tradeoff .side p { font-size: 14.5px; color: var(--ink-2); margin-top: 2px; }
.tradeoff .side:last-child { text-align: right; }
.tradeoff .vs { font-family: var(--f-mono); font-size: 12px; color: var(--ink-3); padding: 4px 8px; border: 1px dashed var(--line-strong); border-radius: 8px; }
@media (max-width: 620px) { .tradeoff { grid-template-columns: 1fr; text-align: left; } .tradeoff .side:last-child { text-align: left; } .tradeoff .vs { justify-self: start; } }

/* ---------- words to know ---------- */
.words { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: 10px; }
.word { background: var(--surface); border: 1px solid var(--line); border-radius: var(--r-m); padding: 12px 14px; }
.word dt { font-family: var(--f-mono); font-weight: 700; font-size: 14px; color: var(--blue); }
.word dd { margin: 4px 0 0; font-size: 15px; color: var(--ink-2); }

/* ---------- quiz ---------- */
.quiz { display: flex; flex-direction: column; gap: 14px; }
.q { background: var(--surface); border: 1px solid var(--line); border-radius: var(--r-m); padding: 16px; }
.q h3 { font-family: var(--f-body); font-size: 17.5px; font-weight: 700; letter-spacing: 0; line-height: 1.35; }
.q .opts { display: grid; gap: 8px; margin-top: 12px; }
.q .opt { text-align: left; appearance: none; font: 15.5px/1.35 var(--f-body); color: var(--ink); background: var(--surface-2); border: 1.5px solid var(--line); border-radius: 11px; padding: 10px 12px; cursor: pointer; }
.q .opt:hover { border-color: var(--blue); }
.q .opt.right { background: var(--mint-soft); border-color: var(--mint); }
.q .opt.wrong { background: var(--coral-soft); border-color: var(--coral); }
.q .why { margin-top: 10px; font-size: 15px; color: var(--ink-2); }
.score { font-family: var(--f-mono); font-size: 14px; color: var(--ink-2); }

/* ---------- chapter footer ---------- */
.chapter-end { padding-block: 40px 70px; border-top: 1px dashed var(--line-strong); }
.next-card { display: grid; grid-template-columns: auto 1fr auto; gap: 18px; align-items: center; text-decoration: none; color: var(--ink); background: var(--surface); border: 1px solid var(--line); border-radius: var(--r-l); padding: 20px 22px; box-shadow: var(--shadow); }
.next-card:hover { border-color: var(--blue); }
.next-card .num { font-family: var(--f-display); font-weight: 800; font-size: 40px; color: var(--blue); line-height: 1; }
.next-card .t { font-family: var(--f-display); font-size: 22px; font-weight: 700; }
.next-card .s { color: var(--ink-2); font-size: 15px; }
.next-card .arrow { font-size: 26px; }
.end-row { display: flex; flex-wrap: wrap; gap: 12px; align-items: center; justify-content: space-between; margin-bottom: 18px; }

.section-title { display: flex; align-items: baseline; gap: 12px; flex-wrap: wrap; margin-bottom: 18px; }
.section-title h2 { font-size: clamp(26px, 3vw, 34px); }
.section-title p { color: var(--ink-2); }

/* toast */
.toast { position: fixed; left: 50%; bottom: calc(20px + env(safe-area-inset-bottom, 0px)); transform: translateX(-50%) translateY(20px); background: var(--ink); color: var(--bg); padding: 10px 16px; border-radius: 12px; font-weight: 700; font-size: 14.5px; opacity: 0; transition: opacity .2s, transform .2s; z-index: 100; pointer-events: none; max-width: calc(100vw - 32px); }
.toast.show { opacity: 1; transform: translateX(-50%) translateY(0); }

.visually-hidden { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }

/* ---------- library (root page) ---------- */
.shelf { display: grid; grid-template-columns: repeat(auto-fill, minmax(290px, 1fr)); gap: 16px; padding-block: 20px 70px; }
.bookcard { display: grid; grid-template-columns: 72px 1fr; gap: 16px; text-decoration: none; color: var(--ink); background: var(--surface); border: 1px solid var(--line); border-radius: var(--r-l); padding: 18px; box-shadow: var(--shadow); transition: border-color .15s, transform .15s; }
.bookcard:hover { border-color: var(--blue); transform: translateY(-2px); }
.bookcard .spine { border-radius: 6px 10px 10px 6px; background: var(--blue); position: relative; overflow: hidden; min-height: 104px; }
.bookcard .spine::after { content: ""; position: absolute; inset: 0 0 0 8px; border-left: 2px solid var(--surface); opacity: .35; }
.bookcard .spine span { position: absolute; inset: 0; display: grid; place-items: center; writing-mode: vertical-rl; rotate: 180deg; color: var(--on-accent); font-family: var(--f-display); font-weight: 800; font-size: 13px; letter-spacing: .06em; text-transform: uppercase; padding-block: 8px; }
.bookcard.lilac .spine { background: var(--lilac); } .bookcard.mint .spine { background: var(--mint); }
.bookcard.coral .spine { background: var(--coral); } .bookcard.sun .spine { background: var(--sun); }
.bookcard h3 { font-size: 20px; font-weight: 750; }
.bookcard .by { font-size: 13.5px; color: var(--ink-3); font-family: var(--f-mono); margin-top: 2px; }
.bookcard p { font-size: 15px; color: var(--ink-2); margin-top: 8px; }
.bookcard .meter { display: flex; align-items: center; gap: 10px; margin-top: 12px; flex-wrap: wrap; }
.addcard { display: flex; flex-direction: column; gap: 10px; justify-content: center; border: 2px dashed var(--line-strong); border-radius: var(--r-l); padding: 20px; background: transparent; color: var(--ink-2); }
.addcard h3 { font-size: 18px; color: var(--ink); }
.addcard ol { margin: 0; padding-left: 20px; font-size: 14.5px; display: flex; flex-direction: column; gap: 6px; }
.addcard code { background: var(--surface-2); border: 1px solid var(--line); border-radius: 5px; padding: 1px 5px; }