/* ===== Design tokens ===== */
:root {
  --text-xs: clamp(0.75rem, 0.7rem + 0.25vw, 0.875rem);
  --text-sm: clamp(0.875rem, 0.8rem + 0.35vw, 1rem);
  --text-base: clamp(1rem, 0.95rem + 0.25vw, 1.125rem);
  --text-lg: clamp(1.125rem, 1rem + 0.75vw, 1.5rem);
  --text-xl: clamp(1.5rem, 1.2rem + 1.25vw, 2.1rem);
  --text-2xl: clamp(2rem, 1.2rem + 2.5vw, 3.2rem);

  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;
  --space-20: 5rem;
  --space-24: 6rem;

  --radius-sm: 0.375rem;
  --radius-md: 0.625rem;
  --radius-lg: 1rem;
  --radius-xl: 1.25rem;

  --transition-interactive: 180ms cubic-bezier(0.16, 1, 0.3, 1);

  --font-display: 'Cabinet Grotesk', 'Satoshi', sans-serif;
  --font-body: 'Satoshi', 'Inter', sans-serif;
  --font-mono: 'JetBrains Mono', 'SF Mono', monospace;

  --content-wide: 1180px;
}

:root,
[data-theme='light'] {
  --color-bg: #f6f4ef;
  --color-surface: #ffffff;
  --color-surface-2: #fbfaf6;
  --color-surface-offset: #eeebe2;
  --color-divider: #e2ded3;
  --color-border: #d6d1c3;

  --color-text: #201d16;
  --color-text-muted: #6c6656;
  --color-text-faint: #a39c89;
  --color-text-inverse: #f6f4ef;

  /* Primary = small circle / teal */
  --color-primary: #0d7d72;
  --color-primary-hover: #0a6058;
  --color-primary-active: #084b45;
  --color-primary-highlight: #cfe6e2;

  /* Warning tone repurposed = large circle / amber */
  --color-warning: #c2660c;
  --color-warning-hover: #9c500a;
  --color-warning-active: #7a3f08;
  --color-warning-highlight: #f0dcc4;

  --color-error: #a12c4e;
  --color-success: #43703a;

  --shadow-sm: 0 1px 2px rgba(30, 26, 15, 0.06);
  --shadow-md: 0 6px 20px rgba(30, 26, 15, 0.09);
  --shadow-lg: 0 16px 40px rgba(30, 26, 15, 0.14);
}

[data-theme='dark'] {
  --color-bg: #14151a;
  --color-surface: #1a1c22;
  --color-surface-2: #1f2128;
  --color-surface-offset: #22252c;
  --color-divider: #2a2d35;
  --color-border: #33363f;

  --color-text: #e4e2db;
  --color-text-muted: #999585;
  --color-text-faint: #666253;
  --color-text-inverse: #14151a;

  --color-primary: #4fc8ba;
  --color-primary-hover: #6fd6c9;
  --color-primary-active: #8ee2d7;
  --color-primary-highlight: #26433f;

  --color-warning: #f0a35c;
  --color-warning-hover: #f5b979;
  --color-warning-active: #f8cb9a;
  --color-warning-highlight: #4a3524;

  --color-error: #dd7a9c;
  --color-success: #8fbf7e;

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.35);
  --shadow-md: 0 6px 20px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 16px 40px rgba(0, 0, 0, 0.5);
}

/* ===== Base ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  -webkit-text-size-adjust: none;
  text-size-adjust: none;
  -webkit-font-smoothing: antialiased;
  scroll-behavior: smooth;
}

body {
  min-height: 100dvh;
  line-height: 1.6;
  font-family: var(--font-body);
  font-size: var(--text-base);
  color: var(--color-text);
  background-color: var(--color-bg);
  background-image:
    linear-gradient(var(--color-divider) 1px, transparent 1px),
    linear-gradient(90deg, var(--color-divider) 1px, transparent 1px);
  background-size: 42px 42px;
  background-attachment: fixed;
}

img, svg, canvas { display: block; max-width: 100%; }
button, input { font: inherit; color: inherit; }
button { cursor: pointer; background: none; border: none; }

h1, h2, h3, h4 { text-wrap: balance; line-height: 1.15; font-family: var(--font-display); }
p, li { text-wrap: pretty; max-width: 74ch; }

:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 3px;
  border-radius: var(--radius-sm);
}

.mono { font-family: var(--font-mono); font-feature-settings: "tnum"; }

.wrap {
  max-width: var(--content-wide);
  margin: 0 auto;
  padding-inline: var(--space-6);
}

/* ===== Header ===== */
.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  background: color-mix(in oklab, var(--color-bg) 88%, transparent);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--color-divider);
}
.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-block: var(--space-4);
}
.logo {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  text-decoration: none;
  color: var(--color-text);
}
.logo-text {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: var(--text-base);
  letter-spacing: -0.01em;
}
.logo-accent { color: var(--color-primary); }

.header-right {
  display: flex;
  align-items: center;
  gap: var(--space-4);
}
.cross-link {
  font-size: var(--text-xs);
  font-weight: 600;
  color: var(--color-text-muted);
  text-decoration: none;
  border: 1px solid var(--color-border);
  padding: 6px var(--space-3);
  border-radius: var(--radius-md);
  transition: var(--transition-interactive);
  white-space: nowrap;
}
.cross-link:hover { color: var(--color-primary); border-color: var(--color-primary); }
@media (max-width: 720px) {
  .cross-link { display: none; }
}

.theme-toggle {
  display: grid;
  place-items: center;
  width: 36px;
  height: 36px;
  border-radius: var(--radius-md);
  color: var(--color-text-muted);
  border: 1px solid var(--color-border);
  transition: var(--transition-interactive);
}
.theme-toggle:hover { color: var(--color-text); border-color: var(--color-text-faint); }

/* ===== Intro ===== */
.intro {
  padding-block: var(--space-16) var(--space-10);
}
.eyebrow {
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-primary);
  margin-bottom: var(--space-3);
}
.intro h1 {
  font-size: var(--text-2xl);
  font-weight: 700;
  letter-spacing: -0.02em;
  margin-bottom: var(--space-5);
  max-width: 20ch;
}
.lede {
  font-size: var(--text-lg);
  color: var(--color-text-muted);
  max-width: 68ch;
}
.lede strong { color: var(--color-text); }

/* ===== Simulator ===== */
.simulator { padding-block: var(--space-6) var(--space-16); }

.sim-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 320px;
  gap: var(--space-6);
  align-items: start;
}
@media (max-width: 900px) {
  .sim-grid { grid-template-columns: 1fr; }
}

.canvas-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-md);
  overflow: hidden;
}

#simCanvas, #raceCanvas {
  width: 100%;
  height: 460px;
  display: block;
  touch-action: none;
}

.catch-banner {
  margin: 0 var(--space-5);
  padding: var(--space-3) var(--space-4);
  border-radius: var(--radius-md);
  background: var(--color-primary-highlight);
  color: var(--color-text);
  font-size: var(--text-sm);
  font-weight: 600;
  border: 1px solid var(--color-primary);
}

.canvas-toolbar {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-4) var(--space-5);
  border-top: 1px solid var(--color-divider);
  background: var(--color-surface-2);
  flex-wrap: wrap;
}
.toolbar-spacer { flex: 1; }

.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  font-weight: 600;
  padding: var(--space-2) var(--space-4);
  border-radius: var(--radius-md);
  border: 1px solid transparent;
  transition: var(--transition-interactive);
}
.btn-primary {
  background: var(--color-primary);
  color: var(--color-text-inverse);
}
.btn-primary:hover { background: var(--color-primary-hover); }
.btn-ghost {
  background: transparent;
  color: var(--color-text-muted);
  border-color: var(--color-border);
}
.btn-ghost:hover { color: var(--color-text); border-color: var(--color-text-faint); }

.speed-control {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-xs);
  color: var(--color-text-muted);
}
.speed-control input[type="range"] { width: 100px; }
.speed-control #speedValue { color: var(--color-text); min-width: 3ch; }

/* ===== Controls card ===== */
.controls-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-md);
  padding: var(--space-6);
}
.controls-card h2 {
  font-size: var(--text-lg);
  margin-bottom: var(--space-5);
}

.control-group { margin-bottom: var(--space-6); }
.control-label-row {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: var(--space-2);
  margin-bottom: var(--space-2);
}
.control-label-row label { font-size: var(--text-sm); color: var(--color-text-muted); }
.value-chip {
  font-size: var(--text-xs);
  font-weight: 600;
  color: var(--color-text);
  background: var(--color-surface-offset);
  padding: 2px var(--space-2);
  border-radius: var(--radius-sm);
}

input[type="range"] {
  width: 100%;
  appearance: none;
  height: 4px;
  background: var(--color-border);
  border-radius: 999px;
  outline: none;
}
input[type="range"]::-webkit-slider-thumb {
  appearance: none;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--color-primary);
  border: 2px solid var(--color-surface);
  box-shadow: 0 0 0 1px var(--color-primary);
  cursor: pointer;
}
input[type="range"]::-moz-range-thumb {
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--color-primary);
  border: 2px solid var(--color-surface);
  cursor: pointer;
}

.checkbox-group { display: flex; flex-direction: column; gap: var(--space-3); }
.checkbox-row {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  cursor: pointer;
}
.checkbox-row input[type="checkbox"] {
  width: 16px;
  height: 16px;
  accent-color: var(--color-primary);
  flex-shrink: 0;
}
.swatch { width: 12px; height: 12px; border-radius: 3px; flex-shrink: 0; }
.swatch-big { background: var(--color-warning); }
.swatch-small { background: var(--color-primary); }
.swatch-rail { background: var(--color-text-faint); }
.swatch-spoke { background: var(--color-text-faint); opacity: 0.5; }

.stats-block {
  border-top: 1px solid var(--color-divider);
  padding-top: var(--space-5);
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}
.stat-row {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: var(--space-3);
  font-size: var(--text-xs);
}
.stat-label { color: var(--color-text-muted); }
.stat-value { color: var(--color-text); font-weight: 600; }

/* ===== Zeno steps card ===== */
.steps-card {
  margin-top: var(--space-6);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-md);
  padding: var(--space-6) var(--space-6) var(--space-8);
}
.steps-card h2 { font-size: var(--text-lg); margin-bottom: var(--space-3); }
.steps-intro { color: var(--color-text-muted); font-size: var(--text-sm); margin-bottom: var(--space-5); max-width: 76ch; }
.steps-intro .eq { color: var(--color-text); }

.steps-body {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 220px;
  gap: var(--space-6);
  align-items: start;
}
@media (max-width: 800px) {
  .steps-body { grid-template-columns: 1fr; }
}

.steps-table-wrap { overflow-x: auto; }
.steps-table {
  width: 100%;
  border-collapse: collapse;
  font-size: var(--text-xs);
}
.steps-table th {
  text-align: left;
  color: var(--color-text-faint);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  font-size: 10px;
  padding: var(--space-2) var(--space-3);
  border-bottom: 1px solid var(--color-divider);
}
.steps-table td {
  padding: var(--space-2) var(--space-3);
  border-bottom: 1px solid var(--color-divider);
  color: var(--color-text-muted);
  font-family: var(--font-mono);
}
.steps-table tr.step-active td {
  color: var(--color-text);
  background: var(--color-primary-highlight);
  font-weight: 600;
}
.steps-table tr.step-active td:first-child { border-radius: var(--radius-sm) 0 0 var(--radius-sm); }
.steps-table tr.step-active td:last-child { border-radius: 0 var(--radius-sm) var(--radius-sm) 0; }

.steps-visual {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding-top: var(--space-8);
}
.step-bar-row { display: flex; align-items: center; height: 14px; }
.step-bar-fill {
  height: 100%;
  background: var(--color-warning);
  border-radius: 2px 0 0 2px;
  transition: width 120ms linear, background-color 120ms linear;
}
.step-bar-row.step-active .step-bar-fill { background: var(--color-primary); }

.steps-note { color: var(--color-text-muted); font-size: var(--text-sm); margin-top: var(--space-5); }
.steps-note .eq { color: var(--color-text); }

/* ===== Explainer ===== */
.explainer { padding-block: var(--space-10) var(--space-24); }
.explainer h2 {
  font-size: var(--text-xl);
  margin-bottom: var(--space-8);
  max-width: 30ch;
}
.explainer-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 300px;
  gap: var(--space-12);
  align-items: start;
}
@media (max-width: 900px) {
  .explainer-grid { grid-template-columns: 1fr; }
}
.explainer-text h3 {
  font-size: var(--text-lg);
  margin-top: var(--space-8);
  margin-bottom: var(--space-3);
}
.explainer-text h3:first-child { margin-top: 0; }
.explainer-text p { color: var(--color-text-muted); margin-bottom: var(--space-4); }
.explainer-text .eq { color: var(--color-text); }
.eq-block {
  background: var(--color-surface-offset);
  border-left: 3px solid var(--color-primary);
  padding: var(--space-3) var(--space-4);
  border-radius: var(--radius-sm);
  color: var(--color-text);
  font-size: var(--text-sm);
  margin-bottom: var(--space-4);
}
.tips-list {
  list-style: disc;
  padding-left: var(--space-5);
  color: var(--color-text-muted);
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}
.tips-list .eq { color: var(--color-text); }

.side-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-5);
  margin-bottom: var(--space-5);
}
.side-card h4 {
  font-size: var(--text-sm);
  font-weight: 700;
  margin-bottom: var(--space-3);
}
.side-card p { font-size: var(--text-sm); color: var(--color-text-muted); }

.formula-table { width: 100%; border-collapse: collapse; font-size: var(--text-xs); }
.formula-table td {
  padding: var(--space-2) 0;
  border-top: 1px solid var(--color-divider);
  color: var(--color-text-muted);
}
.formula-table td:first-child { padding-right: var(--space-3); }
.formula-table tr:first-child td { border-top: none; }
.formula-table td:last-child { text-align: right; color: var(--color-text); font-weight: 600; }

/* ===== Footer ===== */
.site-footer {
  border-top: 1px solid var(--color-divider);
  padding-block: var(--space-8);
}
.site-footer p { font-size: var(--text-xs); color: var(--color-text-faint); }

/* Series navigation dropdown */

.series-nav {
  position: relative;
}
.series-toggle {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: var(--text-xs);
  font-weight: 600;
  color: var(--color-text-muted);
  background: none;
  border: 1px solid var(--color-border);
  padding: 6px var(--space-3);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: var(--transition-interactive);
  font-family: inherit;
  white-space: nowrap;
}
.series-toggle:hover, .series-toggle[aria-expanded="true"] {
  color: var(--color-primary);
  border-color: var(--color-primary);
}
.series-caret {
  transition: transform 0.15s ease;
}
.series-toggle[aria-expanded="true"] .series-caret {
  transform: rotate(180deg);
}
.series-menu {
  position: absolute;
  top: calc(100% + 8px);
  right: 0;
  min-width: 260px;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  box-shadow: 0 12px 32px rgba(0,0,0,0.14);
  padding: var(--space-2);
  display: none;
  flex-direction: column;
  gap: 2px;
  z-index: 40;
}
.series-menu.open { display: flex; }
.series-menu a {
  display: block;
  padding: 8px 10px;
  border-radius: var(--radius-sm, 6px);
  font-size: var(--text-sm);
  color: var(--color-text);
  text-decoration: none;
  transition: var(--transition-interactive);
}
.series-menu a:hover { background: var(--color-surface-alt, rgba(13,125,114,0.08)); color: var(--color-primary); }
.series-menu a.current { color: var(--color-text-muted); pointer-events: none; font-weight: 600; }
@media (max-width: 720px) {
  .series-toggle { padding: 6px 10px; }
}