/* Snap to Fit design system.
   Layout: one reading column (~68ch) with demo panels that break out wider; sticky step bar on top.
   Identity: two scans, two colours. Teal = the fixed scan (target), orange = the scan that moves (source). */
:root {
  --bg: #F2F4F3;
  --surface: #FFFFFF;
  --ink: #101719;
  --muted: #55626A;
  --rule: #D3DBDC;
  --grid: #E7ECEC;
  --target: #0B8A7A;
  --source: #DD6B12;
  --match: #8A97A3;
  --good: #1E8A3C;
  --bad: #C42B5E;
  --accent: #0B8A7A;
  --accent-ink: #FFFFFF;
  --tint: #E8EFEE;
  --f-display: "Bricolage Grotesque", "Avenir Next", "Segoe UI", sans-serif;
  --f-body: "Atkinson Hyperlegible", "Helvetica Neue", Arial, sans-serif;
  --f-mono: "JetBrains Mono", ui-monospace, Menlo, Consolas, monospace;
  --col: 44rem;
  --wide: 72rem;
  --r: 12px;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0C1214; --surface: #131C1F; --ink: #E5ECEE; --muted: #93A2A8; --rule: #263236; --grid: #1A2427;
    --target: #34C7B2; --source: #FF9A47; --match: #6B7A85; --good: #5BD17A; --bad: #FF6E9A; --accent: #34C7B2;
    --accent-ink: #062521; --tint: #18272A; color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #0C1214; --surface: #131C1F; --ink: #E5ECEE; --muted: #93A2A8; --rule: #263236; --grid: #1A2427;
  --target: #34C7B2; --source: #FF9A47; --match: #6B7A85; --good: #5BD17A; --bad: #FF6E9A; --accent: #34C7B2;
  --accent-ink: #062521; --tint: #18272A; color-scheme: dark;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: calc(env(safe-area-inset-top, 0px) + 64px); }
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }
body { margin: 0; background: var(--bg); color: var(--ink); font-family: var(--f-body); font-size: 1.0625rem; line-height: 1.62; -webkit-text-size-adjust: 100%; }
a { color: var(--accent); text-underline-offset: 2px; }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; border-radius: 4px; }
img, canvas, svg { max-width: 100%; }

/* page frame */
.page { padding-inline: 16px; }
.col { max-width: var(--col); margin-inline: auto; }
.wide { max-width: var(--wide); margin-inline: auto; }

/* step bar */
.stepbar { position: sticky; top: env(safe-area-inset-top, 0px); z-index: 20; background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(8px); -webkit-backdrop-filter: blur(8px); border-bottom: 1px solid var(--rule); }
.stepbar ol { list-style: none; margin: 0 auto; padding: 8px 16px; display: flex; gap: 4px; overflow-x: auto; max-width: var(--wide); scrollbar-width: none; }
.stepbar ol::-webkit-scrollbar { display: none; }
.stepbar a { display: inline-flex; gap: 6px; align-items: baseline; white-space: nowrap; text-decoration: none; color: var(--muted);
  font-size: 0.86rem; padding: 4px 10px; border-radius: 999px; }
.stepbar a b { font-family: var(--f-mono); font-weight: 500; font-size: 0.74rem; color: var(--source); }
.stepbar a:hover, .stepbar a.on { color: var(--ink); background: var(--tint); }

/* hero */
.hero { padding-block: 48px 28px; }
.hero-grid { display: grid; grid-template-columns: minmax(0, 1fr); gap: 28px; align-items: center; }
@media (min-width: 900px) { .hero-grid { grid-template-columns: minmax(0, 0.95fr) minmax(0, 1.05fr); } }
.kicker { font-family: var(--f-mono); font-size: 0.78rem; letter-spacing: 0.08em; text-transform: uppercase; color: var(--muted); margin: 0 0 10px; }
h1 { font-family: var(--f-display); font-weight: 800; font-size: clamp(2.8rem, 8vw, 5.2rem); line-height: 0.95; letter-spacing: -0.02em; margin: 0 0 14px; text-wrap: balance; }
h1 .src { color: var(--source); } h1 .tgt { color: var(--target); }
.lede { font-size: 1.2rem; color: var(--muted); margin: 0 0 18px; max-width: 34rem; }
.legend { display: flex; flex-wrap: wrap; gap: 8px 16px; font-size: 0.92rem; color: var(--muted); }
.dot { display: inline-block; width: 10px; height: 10px; border-radius: 50%; margin-right: 6px; vertical-align: 0.05em; }
.dot.src { background: var(--source); } .dot.tgt { background: var(--target); } .dot.match { background: var(--match); }

/* sections */
.sec { padding-block: 56px 12px; border-top: 1px solid var(--rule); }
.sec-head { margin-bottom: 18px; }
.sec-num { font-family: var(--f-mono); font-size: 0.8rem; color: var(--source); letter-spacing: 0.08em; text-transform: uppercase; margin: 0 0 6px; }
h2 { font-family: var(--f-display); font-weight: 700; font-size: clamp(1.9rem, 4.4vw, 2.7rem); line-height: 1.05; letter-spacing: -0.01em; margin: 0 0 12px; text-wrap: balance; }
h3 { font-family: var(--f-display); font-weight: 700; font-size: 1.35rem; line-height: 1.2; margin: 30px 0 8px; text-wrap: balance; }
p { margin: 0 0 14px; }
ul, ol { padding-left: 1.3rem; margin: 0 0 14px; } li { margin-bottom: 5px; }
.slide-ref { font-family: var(--f-mono); font-size: 0.76rem; color: var(--muted); border: 1px solid var(--rule); border-radius: 999px; padding: 1px 8px; white-space: nowrap; }

/* demo panel */
.demo { background: var(--surface); border: 1px solid var(--rule); border-radius: var(--r); padding: 14px; margin-block: 18px 26px; }
.demo-grid { display: grid; grid-template-columns: minmax(0, 1fr); gap: 14px; }
@media (min-width: 900px) { .demo-grid { grid-template-columns: minmax(0, 1fr) 18.5rem; } }
.stage { position: relative; min-width: 0; }
canvas.plot { display: block; width: 100%; aspect-ratio: 16 / 10; background: var(--bg); border-radius: 8px; border: 1px solid var(--rule); touch-action: none; }
canvas.plot.square { aspect-ratio: 1 / 1; }
canvas.chart { display: block; width: 100%; height: 150px; }
.controls { display: grid; gap: 10px; align-content: start; min-width: 0; }
.ctl { display: grid; grid-template-columns: 1fr auto; gap: 2px 10px; align-items: center; font-size: 0.9rem; }
.ctl input[type=range] { grid-column: 1 / -1; width: 100%; accent-color: var(--accent); }
.ctl-label { color: var(--muted); }
.ctl-label { grid-row: 1; grid-column: 1; }
.ctl-val { grid-row: 1; grid-column: 2; font-family: var(--f-mono); font-size: 0.82rem; font-variant-numeric: tabular-nums; }
.tgl { display: flex; gap: 8px; align-items: center; font-size: 0.92rem; cursor: pointer; }
.tgl input { accent-color: var(--accent); width: 16px; height: 16px; }
.btns { display: flex; flex-wrap: wrap; gap: 8px; }
.btn { font: inherit; font-size: 0.92rem; font-weight: 700; padding: 8px 14px; border-radius: 8px; border: 1px solid var(--rule); background: var(--bg); color: var(--ink); cursor: pointer; }
.btn:hover { border-color: var(--accent); }
.btn-primary { background: var(--accent); color: var(--accent-ink); border-color: var(--accent); }
.btn-primary:hover { filter: brightness(1.06); }
.btn[disabled] { opacity: 0.5; cursor: default; }
select { font: inherit; font-size: 0.92rem; padding: 6px 8px; border-radius: 8px; border: 1px solid var(--rule); background: var(--bg); color: var(--ink); }
.readout { font-family: var(--f-mono); font-size: 0.84rem; font-variant-numeric: tabular-nums; background: var(--bg); border: 1px solid var(--rule); border-radius: 8px; padding: 8px 10px; line-height: 1.55; overflow-x: auto; }
.readout b { color: var(--ink); font-weight: 600; } .readout .k { color: var(--muted); }
.good { color: var(--good); } .bad { color: var(--bad); }
.caption { font-size: 0.9rem; color: var(--muted); margin: 8px 2px 0; }
.try { font-size: 0.95rem; border-left: 3px solid var(--source); padding: 2px 0 2px 12px; margin: 10px 0 0; }
.try b { font-family: var(--f-mono); font-size: 0.72rem; letter-spacing: 0.1em; text-transform: uppercase; color: var(--source); margin-right: 6px; }

/* matrices */
.mat-wrap { display: inline-flex; align-items: center; gap: 6px; margin: 2px 8px 2px 0; vertical-align: middle; }
.mat-label { font-family: var(--f-mono); font-size: 0.82rem; color: var(--muted); }
table.mat { border-collapse: collapse; font-family: var(--f-mono); font-size: 0.8rem; font-variant-numeric: tabular-nums;
  border-left: 1.5px solid var(--ink); border-right: 1.5px solid var(--ink); border-radius: 3px; }
table.mat td { padding: 1px 7px; text-align: right; }

/* stepper */
.stepper { display: grid; gap: 10px; }
.steps { list-style: none; padding: 0; margin: 0; display: grid; gap: 6px; counter-reset: s; }
.steps li { counter-increment: s; display: grid; grid-template-columns: 26px 1fr; gap: 8px; padding: 8px 10px; border-radius: 8px; border: 1px solid var(--rule); background: var(--bg); color: var(--muted); }
.steps li::before { content: counter(s); font-family: var(--f-mono); font-size: 0.8rem; width: 22px; height: 22px; border-radius: 50%; display: grid; place-items: center; border: 1px solid var(--rule); }
.steps li.on { color: var(--ink); border-color: var(--source); }
.steps li.on::before { background: var(--source); color: var(--surface); border-color: var(--source); }
.steps li.done::before { background: var(--tint); color: var(--ink); }

/* callouts */
.note, .trap { border-radius: 10px; padding: 12px 14px; margin: 16px 0; }
.note { background: var(--tint); }
.trap { background: color-mix(in srgb, var(--bad) 12%, var(--surface)); }
.note > b:first-child, .trap > b:first-child { display: block; font-family: var(--f-mono); font-size: 0.72rem; letter-spacing: 0.1em; text-transform: uppercase; margin-bottom: 3px; }
.note > b:first-child { color: var(--accent); } .trap > b:first-child { color: var(--bad); }
.note p:last-child, .trap p:last-child { margin-bottom: 0; }

/* formulas */
.formula { background: var(--surface); border: 1px solid var(--rule); border-radius: 10px; padding: 8px 14px; margin: 14px 0; overflow-x: auto; }
mjx-container[display="true"] { margin: 6px 0 !important; }

/* tables */
.tbl { overflow-x: auto; border: 1px solid var(--rule); border-radius: 10px; background: var(--surface); margin: 14px 0; }
.tbl table { border-collapse: collapse; width: 100%; font-size: 0.92rem; }
.tbl th, .tbl td { text-align: left; padding: 8px 10px; border-bottom: 1px solid var(--rule); vertical-align: top; }
.tbl th { font-family: var(--f-mono); font-size: 0.72rem; letter-spacing: 0.06em; text-transform: uppercase; color: var(--muted); background: var(--tint); }
.tbl tr:last-child td { border-bottom: 0; }
.tbl td.num { font-family: var(--f-mono); font-variant-numeric: tabular-nums; text-align: right; }

/* quiz */
.q { padding-block: 12px; border-top: 1px solid var(--rule); }
.q:first-of-type { border-top: 0; }
.q .stem { font-weight: 700; margin-bottom: 8px; }
.opts { display: grid; gap: 6px; }
.opts button { text-align: left; font: inherit; font-size: 0.97rem; padding: 8px 12px; border-radius: 8px; border: 1px solid var(--rule); background: var(--bg); color: var(--ink); cursor: pointer; }
.opts button.right { border-color: var(--good); background: color-mix(in srgb, var(--good) 14%, var(--surface)); }
.opts button.wrong { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 14%, var(--surface)); }
.why { font-size: 0.95rem; color: var(--muted); margin-top: 8px; }

footer.site { padding-block: 40px 60px; color: var(--muted); font-size: 0.9rem; border-top: 1px solid var(--rule); margin-top: 40px; }
@media (max-width: 520px) { body { font-size: 1rem; } .demo { padding: 10px; } h2 { font-size: 1.85rem; } }