:root {
  /* Palette from https://theonovak.com/assets/theme.css (2026-10-15). */
  color-scheme: dark;
  --background: #060807;
  --surface: #0d1410;
  --ink: #e4ece6;
  --muted: #8fa896;
  --accent: #58c08a;
  --accent-hover: #7ad4a8;
  --gold: #c9a45c;
  --line: rgba(150, 180, 158, 0.13);
  --wash: #141e18;
  --good: #7ad4a8;
  --bad: #d47878;
  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
  font-size: 16px;
  line-height: 1.55;
  background: var(--background);
  color: var(--ink);
}

* { box-sizing: border-box; }
body { margin: 0; min-width: 0; }
button, input { font: inherit; }
button { cursor: pointer; }
a { color: var(--accent-hover); }
:focus-visible { outline: 3px solid var(--gold); outline-offset: 3px; }
[hidden] { display: none !important; }

.site-header {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem max(1.25rem, calc((100vw - 72rem) / 2));
  border-bottom: 1px solid var(--line);
}
.wordmark { color: var(--ink); font-weight: 720; text-decoration: none; letter-spacing: -0.025em; }
.site-header p, footer p { margin: 0; color: var(--muted); font-size: .9rem; }
main { width: min(72rem, 100%); margin: 0 auto; padding: 3.25rem 1.5rem 4rem; }
.intro { max-width: 49rem; margin: 0 0 2.75rem; }
.eyebrow { margin: 0 0 .7rem; color: var(--accent-hover); font-weight: 650; }
h1, h2, h3, p { overflow-wrap: anywhere; }
h1 { max-width: 16ch; margin: 0; font-size: clamp(2rem, 5vw, 3.45rem); line-height: 1.06; letter-spacing: -.045em; }
.intro > p:last-child { max-width: 58ch; margin: 1rem 0 0; color: var(--muted); font-size: 1.1rem; }
.workspace { display: grid; grid-template-columns: minmax(14rem, .72fr) minmax(0, 1.55fr); gap: clamp(2rem, 5vw, 5rem); align-items: start; }
.module-map h2 { margin: 0 0 1.15rem; font-size: 1.18rem; }
.module-map ol { margin: 0; padding: 0; list-style: none; }
.module { position: relative; display: grid; grid-template-columns: 2rem minmax(0, 1fr); gap: .8rem; min-width: 0; padding: 0 0 1.3rem; }
.module:not(:last-child)::before { position: absolute; top: 2rem; bottom: 0; left: .95rem; width: 1px; background: var(--line); content: ""; }
.module-index { display: grid; width: 2rem; height: 2rem; place-items: center; border: 1px solid var(--muted); border-radius: 50%; color: var(--muted); font-size: .88rem; }
.current .module-index { border-color: var(--accent); background: var(--accent); color: var(--background); }
.module h3 { margin: 0; font-size: 1rem; }
.module p { margin: .1rem 0 0; color: var(--muted); font-size: .9rem; }
.future { color: var(--muted); }
.start-button, .button { min-height: 2.75rem; border: 1px solid transparent; border-radius: .35rem; padding: .55rem 1rem; font-weight: 650; }
.start-button { margin-top: .8rem; background: var(--accent); color: var(--background); }
.start-button:hover, .primary:hover { background: var(--accent-hover); }
.lesson { min-width: 0; padding: 1.25rem clamp(1rem, 3vw, 2rem) 1.5rem; border: 1px solid var(--line); border-top: 4px solid var(--accent); background: var(--surface); }
.reset-note { margin: 0 0 1.25rem; color: var(--muted); font-size: .9rem; }
.step-line { display: flex; flex-wrap: wrap; justify-content: space-between; gap: .5rem 1rem; padding-bottom: .8rem; border-bottom: 1px solid var(--line); color: var(--muted); font-size: .9rem; }
.stage-title { margin: 1.15rem 0 .8rem; font-size: clamp(1.45rem, 3vw, 1.9rem); line-height: 1.2; letter-spacing: -.025em; }
.stage-copy { max-width: 68ch; }
.stage-copy p { margin: .7rem 0; }
.question { margin: 1.5rem 0 0; padding: 1rem 0; border-top: 1px solid var(--line); }
.question h3 { margin: 0 0 .7rem; font-size: 1.02rem; }
.answer-form { display: flex; flex-wrap: wrap; align-items: end; gap: .65rem; }
.answer-form label, .range-control label { display: grid; gap: .25rem; font-weight: 600; }
.answer-form input[type="text"] { width: min(16rem, 100%); min-height: 2.7rem; border: 1px solid var(--muted); border-radius: .3rem; padding: .45rem .6rem; background: var(--background); color: var(--ink); }
.answer-form fieldset { display: grid; gap: .5rem; width: 100%; margin: 0; border: 0; padding: 0; }
.answer-form legend { margin-bottom: .45rem; font-weight: 600; }
.choice-option { display: flex; align-items: flex-start; gap: .5rem; font-weight: 400; }
.choice-option input { margin-top: .3rem; accent-color: var(--accent); }
.button { background: var(--accent); color: var(--background); }
.secondary { border-color: var(--muted); background: var(--surface); color: var(--ink); }
.secondary:hover { background: var(--wash); }
.text-button { border: 0; padding: .3rem .1rem; background: transparent; color: var(--accent-hover); font-weight: 650; text-decoration: underline; text-underline-offset: .2em; }
.help-actions { display: flex; flex-wrap: wrap; gap: .6rem 1.25rem; margin-top: .7rem; }
.feedback { min-height: 1.5em; margin: .75rem 0 0; }
.feedback[data-kind="correct"] { color: var(--good); }
.feedback[data-kind="incorrect"], .feedback[data-kind="invalid"] { color: var(--bad); }
.revealed { margin: .6rem 0 0; padding: .7rem .85rem; border-left: 3px solid var(--gold); background: var(--wash); }
.graph-panel { margin: 1.4rem 0 0; padding: 1rem; background: var(--wash); }
.graph-panel h3 { margin: 0 0 .7rem; font-size: 1rem; }
.graph-wrap { min-width: 0; }
.graph { display: block; width: 100%; height: auto; overflow: visible; }
.plot-bg { fill: var(--surface); stroke: var(--line); }
.axis { stroke: var(--muted); stroke-width: 1.2; }
.curve { fill: none; stroke: var(--accent); stroke-width: 3; }
.secant { fill: none; stroke: var(--gold); stroke-width: 2.7; }
.tangent { fill: none; stroke: var(--ink); stroke-width: 2.5; stroke-dasharray: 8 6; }
.point { fill: var(--gold); stroke: var(--surface); stroke-width: 2; }
.point-next { fill: var(--accent); stroke: var(--surface); stroke-width: 2; }
.graph text { fill: var(--ink); font-family: inherit; font-size: 13px; }
.legend { display: flex; flex-wrap: wrap; gap: .35rem 1.1rem; margin: .6rem 0 0; color: var(--muted); font-size: .88rem; }
.legend span { display: inline-flex; align-items: center; gap: .4rem; }
.key-line { width: 1.4rem; border-top: 3px solid var(--accent); }
.key-line.secant-key { border-color: var(--gold); }
.key-line.tangent-key { border-color: var(--ink); border-top-style: dashed; }
.range-controls { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: .8rem 1.3rem; margin-top: 1rem; }
.range-control { min-width: 0; }
.range-control output { display: block; color: var(--muted); font-variant-numeric: tabular-nums; }
.range-control input { width: 100%; accent-color: var(--accent); }
.graph-values { margin: .85rem 0 0; font-variant-numeric: tabular-nums; }
.graph-values p { margin: .25rem 0; }
.stage-controls { display: flex; flex-wrap: wrap; justify-content: space-between; gap: .7rem; margin-top: 1.5rem; padding-top: 1rem; border-top: 1px solid var(--line); }
.recap-list { display: grid; gap: .75rem; margin: 1.2rem 0; padding: 0; list-style: none; }
.recap-item { padding: .8rem 0; border-bottom: 1px solid var(--line); }
.recap-item p { margin: .15rem 0; }
.recap-item button { margin-top: .35rem; }
.recommendation { padding: .9rem 1rem; border-left: 3px solid var(--gold); background: var(--wash); }
.reflection-options { display: grid; gap: .5rem; margin: .9rem 0; }
.noscript { max-width: 72rem; margin: 0 auto 1rem; padding: 1rem 1.5rem; color: var(--bad); }
footer { border-top: 1px solid var(--line); padding: 1.25rem; text-align: center; }

@media (max-width: 48rem) {
  main { padding: 2.25rem 1rem 3rem; }
  .site-header { align-items: flex-start; flex-direction: column; gap: .1rem; padding: .85rem 1rem; }
  .workspace { grid-template-columns: minmax(0, 1fr); gap: 2rem; }
  .module-map ol { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); column-gap: 1rem; }
  .module:not(:last-child)::before { display: none; }
}
@media (max-width: 25rem) {
  .module-map ol, .range-controls { grid-template-columns: minmax(0, 1fr); }
  .lesson { padding-inline: .85rem; }
  .answer-form { align-items: stretch; flex-direction: column; }
  .answer-form input[type="text"] { width: 100%; }
}