/* CarMechanix design system.
 * Dark ground. Blueprint blue is structural ink. One UI accent (teal).
 * Material-state colours live ONLY inside figures, never in chrome.
 * Type: Space Grotesk (display), Inter (read), JetBrains Mono (measured values).
 */
:root {
  color-scheme: dark;
  --bg: #090c12;
  --bg-2: #0c1017;
  --panel: #10151f;
  --panel-2: #141b28;
  --ink: #eaeef5;
  --ink-soft: #9aa7ba;
  --ink-faint: #63708440;
  --ink-mute: #647084;
  --line: #232f42;
  --line-2: #2c3a52;
  --grid: #1a2434;
  --blue: #57c1ff;         /* structural ink */
  --blue-dim: #3a6d92;
  --accent: #4fd6b8;       /* single UI accent */
  --accent-ink: #05221c;
  /* material-state, figures only */
  --m-fresh: #6bd0ff;
  --m-spark: #ffd24d;
  --m-fire: #ff7a3c;
  --m-spent: #8593a6;
  --m-fuel: #e0a35c;
  --display: "Bricolage Grotesque", system-ui, sans-serif;
  --sans: "Inter", system-ui, -apple-system, sans-serif;
  --mono: "JetBrains Mono", ui-monospace, Menlo, Consolas, monospace;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  margin: 0; background: var(--bg); color: var(--ink);
  font-family: var(--sans); font-size: 17px; line-height: 1.65;
  -webkit-font-smoothing: antialiased; text-rendering: optimizeLegibility;
}
.wrap { max-width: 1120px; margin: 0 auto; padding: 0 1.5rem; }
a { color: var(--accent); text-underline-offset: 3px; }

/* ---- top bar ---- */
.top { position: sticky; top: 0; z-index: 40; border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--bg) 84%, transparent); backdrop-filter: blur(10px); }
.top-row { display: flex; align-items: center; justify-content: space-between; height: 56px; }
.home { font-family: var(--mono); font-size: .72rem; letter-spacing: .06em;
  color: var(--ink-mute); text-decoration: none; }
.home:hover { color: var(--accent); }
.wordmark { font-family: var(--display); font-weight: 700; letter-spacing: .01em;
  font-size: 1.02rem; margin: 0; }
.wordmark span { color: var(--blue); }

/* ---- hero ---- */
.hero { padding: clamp(2.5rem, 6vw, 5rem) 0 2rem; }
.hero-grid { display: grid; grid-template-columns: 1fr; gap: 2rem; align-items: center; }
@media (min-width: 900px) { .hero-grid { grid-template-columns: 0.86fr 1.14fr; gap: 3rem; } }

.kicker { font-family: var(--mono); font-size: .72rem; letter-spacing: .14em;
  text-transform: uppercase; color: var(--accent); margin: 0 0 1.1rem; }
h1 { font-family: var(--display); font-weight: 600; letter-spacing: -.02em;
  font-size: clamp(2.3rem, 5.5vw, 3.7rem); line-height: 1.03; margin: 0 0 1.2rem; text-wrap: balance; }
h1 em { font-style: italic; color: var(--blue); }
.hero-lede { font-size: 1.15rem; color: var(--ink-soft); max-width: 42ch; margin: 0 0 1.6rem; }
.hero-note { font-family: var(--mono); font-size: .76rem; color: var(--ink-mute);
  border-left: 2px solid var(--line-2); padding-left: .9rem; max-width: 40ch; }

/* ---- the cylinder figure ---- */
.figure { background:
    radial-gradient(130% 110% at 60% 0%, var(--panel-2), var(--bg-2) 72%);
  border: 1px solid var(--line); border-radius: 16px; padding: 1rem 1rem 1.2rem;
  box-shadow: 0 30px 80px -40px rgba(0,0,0,.8); }
.cyl-svg { display: block; width: 100%; max-width: 380px; height: auto; margin: 0 auto; }

.cyl-block { fill: none; stroke: var(--blue-dim); stroke-width: 1.4; opacity: .55; }
.cyl-jacket line { stroke: var(--m-fresh); stroke-width: 2; opacity: .4; }
.cyl-wall { stroke: var(--blue); stroke-width: 2.5; }
.cyl-head { stroke: var(--blue); stroke-width: 3; fill: none; }
.cyl-charge { transition: none; }
.cyl-port { fill: none; stroke: var(--blue-dim); stroke-width: 6; opacity: .3; stroke-linecap: round; }
.cyl-valve line { stroke: #aeb9cc; }
.cyl-valve path { fill: #8492a8; stroke: none; }
.cyl-valve.is-open path { fill: var(--m-fresh); }
.cyl-vlabel { font-family: var(--mono); font-size: 11px; fill: var(--ink-mute); }
.cyl-plug { stroke: var(--m-spark); stroke-linecap: round; }
.cyl-rod { stroke: #9fb0c9; }
.cyl-case { fill: #0d131d; stroke: var(--line-2); stroke-width: 1.5; }
.cyl-crank { stroke: #c2cee0; }
.cyl-pin { fill: var(--accent); }
.cyl-hub { fill: #7d8ba0; }

/* figure panel */
.cyl-panel { max-width: 380px; margin: 1rem auto 0; }
.cyl-strokes { display: grid; grid-template-columns: repeat(4, 1fr); gap: .3rem; margin-bottom: .7rem; }
.cyl-stroke { font-family: var(--mono); font-size: .64rem; letter-spacing: .02em;
  color: var(--ink-mute); background: var(--panel); border: 1px solid var(--line);
  border-radius: 6px; padding: .45rem .2rem; cursor: pointer; display: flex; flex-direction: column;
  align-items: center; gap: .32rem; text-transform: capitalize; transition: color .15s, border-color .15s; }
.cyl-sw { width: 14px; height: 4px; border-radius: 2px; background: var(--ink-mute); }
.cyl-stroke[data-stroke="intake"] .cyl-sw { background: var(--m-fresh); }
.cyl-stroke[data-stroke="compression"] .cyl-sw { background: #7aa7d8; }
.cyl-stroke[data-stroke="power"] .cyl-sw { background: var(--m-fire); }
.cyl-stroke[data-stroke="exhaust"] .cyl-sw { background: var(--m-spent); }
.cyl-stroke.is-on { color: var(--ink); border-color: var(--accent); background: var(--panel-2); }

.cyl-track { position: relative; height: 12px; border-radius: 6px; overflow: hidden;
  display: flex; margin-bottom: .8rem; cursor: pointer; border: 1px solid var(--line); }
.cyl-band { flex: 1; opacity: .5; }
.cyl-b-intake { background: var(--m-fresh); }
.cyl-b-compression { background: #7aa7d8; }
.cyl-b-power { background: var(--m-fire); }
.cyl-b-exhaust { background: var(--m-spent); }
.cyl-playhead { position: absolute; top: -3px; bottom: -3px; width: 2px; background: #fff;
  box-shadow: 0 0 6px rgba(255,255,255,.7); transform: translateX(-1px); }

.cyl-ctrls { display: flex; align-items: center; gap: .5rem; }
.cyl-btn { font-family: var(--mono); font-size: .74rem; color: var(--ink-soft);
  background: var(--panel); border: 1px solid var(--line); border-radius: 7px;
  padding: .42rem .7rem; cursor: pointer; transition: color .15s, border-color .15s; }
.cyl-btn:hover { color: var(--ink); border-color: var(--line-2); }
.cyl-btn.is-on { color: var(--accent); border-color: var(--accent); }
.cyl-reading { margin-left: auto; display: flex; align-items: baseline; gap: .6rem; }
.cyl-deg { font-family: var(--mono); font-size: 1rem; color: var(--ink); }
.cyl-hint { font-family: var(--mono); font-size: .66rem; color: var(--ink-mute); }

/* ---- shared figure controls (every interactive figure uses these) ---- */
.fig-svg { display: block; width: 100%; max-width: 520px; height: auto; margin: 0 auto; }
.fig-panel { max-width: 520px; margin: 1rem auto 0; }
.fig-ctrls { display: flex; align-items: center; gap: .55rem; flex-wrap: wrap; }
.fig-btn { font-family: var(--mono); font-size: .74rem; color: var(--ink-soft);
  background: var(--panel); border: 1px solid var(--line); border-radius: 7px;
  padding: .42rem .7rem; cursor: pointer; transition: color .15s, border-color .15s; }
.fig-btn:hover { color: var(--ink); border-color: var(--line-2); }
.fig-btn.is-on { color: var(--accent); border-color: var(--accent);
  background: color-mix(in srgb, var(--accent) 12%, var(--panel)); }
.fig-slider { flex: 1; min-width: 120px; accent-color: var(--accent); height: 4px; }
.fig-label { font-family: var(--mono); font-size: .68rem; letter-spacing: .04em;
  text-transform: uppercase; color: var(--ink-mute); }
.fig-reading { margin-left: auto; display: flex; align-items: baseline; gap: .5rem; }
.fig-val { font-family: var(--mono); font-size: 1rem; color: var(--ink); }
.fig-legend { display: flex; gap: 1.1rem; flex-wrap: wrap; font-family: var(--mono);
  font-size: .68rem; color: var(--ink-mute); margin-top: .7rem; }
.fig-legend i { display: inline-block; width: 12px; height: 3px; border-radius: 2px;
  margin-right: .35rem; vertical-align: middle; }

/* ---- chapters / narrative ---- */
.chapter { padding: clamp(2.4rem, 6vw, 4.4rem) 0; border-top: 1px solid var(--line); }
.ch-num { font-family: var(--mono); font-size: .72rem; letter-spacing: .12em; color: var(--accent);
  margin: 0 0 .8rem; }
.ch-h { font-family: var(--display); font-weight: 600; font-size: clamp(1.6rem, 3.4vw, 2.4rem);
  letter-spacing: -.015em; line-height: 1.08; margin: 0 0 1rem; text-wrap: balance; }
.ch-body { color: var(--ink-soft); max-width: 58ch; }
.ch-body p { margin: 0 0 1rem; }
.ch-body strong { color: var(--ink); font-weight: 600; }

.ch-split { display: grid; grid-template-columns: 1fr; gap: 2rem; align-items: center; }
@media (min-width: 900px) {
  .ch-split { grid-template-columns: 0.9fr 1.1fr; gap: 3rem; }
  .ch-split.flip .ch-text { order: 2; }
}
.ch-wide .ch-text { max-width: 62ch; margin: 0 auto 2rem; text-align: center; }
.ch-wide .ch-body { max-width: 62ch; margin-left: auto; margin-right: auto; }

/* connective beat: narrow prose between figures */
.beat { padding: clamp(2rem, 5vw, 3.4rem) 0; border-top: 1px solid var(--line); }
.beat-inner { max-width: 46ch; }
.beat p { color: var(--ink-soft); font-size: 1.12rem; margin: 0 0 1rem; }
.beat strong { color: var(--ink); }
.beat .lead { font-family: var(--display); font-weight: 500; font-size: clamp(1.3rem, 2.6vw, 1.7rem);
  color: var(--ink); line-height: 1.2; letter-spacing: -.01em; margin: 0 0 1.1rem; }

/* ---- the rest of the car: cards ---- */
.rest { padding: clamp(2.4rem, 6vw, 4rem) 0 1rem; border-top: 1px solid var(--line); }
.section-h { font-family: var(--display); font-weight: 600; font-size: clamp(1.5rem, 3vw, 2.1rem);
  letter-spacing: -.01em; margin: 0 0 .5rem; }
.section-sub { color: var(--ink-soft); max-width: 60ch; margin: 0 0 1.6rem; }
.card-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(250px, 1fr)); gap: .8rem; }
.card { background: var(--panel); border: 1px solid var(--line); border-radius: 12px; padding: 1.2rem 1.3rem; }
.card h3 { font-family: var(--display); font-weight: 600; font-size: 1.05rem; margin: 0 0 .4rem; }
.card .card-tag { font-family: var(--mono); font-size: .64rem; letter-spacing: .1em; text-transform: uppercase;
  color: var(--blue); margin: 0 0 .7rem; }
.card p { color: var(--ink-soft); font-size: .92rem; margin: 0; }

/* ---- lesson framing ---- */
.progress { position: sticky; top: 56px; z-index: 30; height: 3px; background: var(--line);
  overflow: hidden; }
.progress-fill { height: 100%; width: 0; background: var(--accent);
  box-shadow: 0 0 10px color-mix(in srgb, var(--accent) 60%, transparent); }

.cover { min-height: calc(100dvh - 59px); display: flex; align-items: center;
  padding: 2rem 0 3rem; }
.cover-grid { display: grid; grid-template-columns: 1fr; gap: 2.4rem; align-items: center; width: 100%; }
@media (min-width: 900px) { .cover-grid { grid-template-columns: 1.05fr 0.95fr; gap: 3.5rem; } }
.lesson-tag { font-family: var(--mono); font-size: .74rem; letter-spacing: .16em;
  text-transform: uppercase; color: var(--accent); margin: 0 0 1.1rem; display: flex; gap: .8rem; align-items: center; }
.lesson-tag .dot { width: 5px; height: 5px; border-radius: 50%; background: var(--accent); }
.cover h1 { font-family: var(--display); font-weight: 700; letter-spacing: -.025em;
  font-size: clamp(2.6rem, 7vw, 4.6rem); line-height: 0.98; margin: 0 0 1.3rem; text-wrap: balance; }
.cover h1 em { font-style: italic; color: var(--blue); }
.cover-lede { font-size: 1.2rem; color: var(--ink-soft); max-width: 46ch; margin: 0 0 2rem; }
.objectives { list-style: none; margin: 0 0 2rem; padding: 0; display: grid; gap: .55rem; max-width: 44ch; }
.objectives li { position: relative; padding-left: 1.7rem; color: var(--ink-soft); font-size: .96rem; }
.objectives li::before { content: ""; position: absolute; left: 0; top: .55rem; width: 9px; height: 9px;
  border: 1.5px solid var(--accent); border-radius: 2px; }
.start-row { display: flex; align-items: center; gap: 1.2rem; flex-wrap: wrap; }
.start-btn { font-family: var(--display); font-weight: 600; font-size: 1rem; cursor: pointer;
  color: var(--accent-ink); background: var(--accent); border: none; border-radius: 9px;
  padding: .85rem 1.5rem; transition: transform .1s, filter .15s; }
.start-btn:hover { filter: brightness(1.07); }
.start-btn:active { transform: translateY(1px); }
.start-meta { font-family: var(--mono); font-size: .76rem; color: var(--ink-mute); }

/* part header + key idea */
.part-tag { font-family: var(--mono); font-size: .72rem; letter-spacing: .12em; text-transform: uppercase;
  color: var(--accent); margin: 0 0 .8rem; }
.key-idea { border-left: 2px solid var(--accent); background: color-mix(in srgb, var(--accent) 7%, transparent);
  border-radius: 0 8px 8px 0; padding: .9rem 1.1rem; margin-top: 1.4rem; }
.key-idea b { font-family: var(--mono); font-size: .66rem; letter-spacing: .12em; text-transform: uppercase;
  color: var(--accent); display: block; margin-bottom: .3rem; }
.key-idea span { color: var(--ink); font-size: .98rem; }

/* recap + self check */
.recap { padding: clamp(3rem, 7vw, 5rem) 0; border-top: 1px solid var(--line);
  background: radial-gradient(120% 90% at 50% 0%, var(--bg-2), var(--bg) 70%); }
.recap-badge { font-family: var(--mono); font-size: .74rem; letter-spacing: .14em; text-transform: uppercase;
  color: var(--accent); margin: 0 0 1rem; }
.recap h2 { font-family: var(--display); font-weight: 700; font-size: clamp(1.8rem, 4vw, 2.8rem);
  letter-spacing: -.02em; margin: 0 0 1.4rem; text-wrap: balance; }
.recap-list { list-style: none; margin: 0 0 2.4rem; padding: 0; display: grid; gap: .6rem; max-width: 60ch; }
.recap-list li { position: relative; padding-left: 1.9rem; color: var(--ink-soft); }
.recap-list li::before { content: "\2713"; position: absolute; left: 0; top: 0; color: var(--accent);
  font-weight: 700; }
.quiz { display: grid; gap: 1rem; max-width: 60ch; }
.q { background: var(--panel); border: 1px solid var(--line); border-radius: 12px; padding: 1.2rem 1.3rem; }
.q-ask { font-weight: 600; color: var(--ink); margin: 0 0 .9rem; }
.q-opts { display: grid; gap: .5rem; }
.q-opt { text-align: left; font-family: inherit; font-size: .95rem; color: var(--ink-soft);
  background: var(--bg-2); border: 1px solid var(--line); border-radius: 8px; padding: .6rem .8rem; cursor: pointer;
  transition: border-color .15s, color .15s, background .15s; }
.q-opt:hover { border-color: var(--line-2); color: var(--ink); }
.q-opt.correct { border-color: var(--accent); background: color-mix(in srgb, var(--accent) 12%, var(--bg-2)); color: var(--ink); }
.q-opt.wrong { border-color: #c9584f; background: color-mix(in srgb, #c9584f 12%, var(--bg-2)); }
.q-opt:disabled { cursor: default; }
.q-fb { font-size: .88rem; color: var(--ink-mute); margin: .8rem 0 0; min-height: 1px; }
.q-fb.show { color: var(--ink-soft); }

/* ---- scroll reveal (motion: reveal each beat as the reader reaches it) ---- */
.reveal { opacity: 0; transform: translateY(18px); transition: opacity .7s cubic-bezier(.16,1,.3,1), transform .7s cubic-bezier(.16,1,.3,1); }
.reveal.in { opacity: 1; transform: none; }
@media (prefers-reduced-motion: reduce) { .reveal { opacity: 1; transform: none; transition: none; } }

/* footer */
.foot { border-top: 1px solid var(--line); padding: 2.4rem 0 4rem; color: var(--ink-mute); margin-top: 3rem; }
.foot p { max-width: 68ch; font-size: .9rem; margin: 0 0 .6rem; }
.foot-links { font-family: var(--mono); font-size: .8rem; }

@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }