/* ============================================
   PLANE & POINT — Design tokens & base
   ============================================ */

:root, [data-theme="light"] {
  /* Surfaces — white + cool neutrals */
  --color-bg: #ffffff;
  --color-surface: #ffffff;
  --color-surface-2: #f7f9fc;
  --color-surface-offset: #eef2f8;
  --color-border: #cfd6e0;
  --color-divider: #dde3ec;
  --color-grid: #dae0eb;
  --color-grid-strong: #a8b3c5;

  /* Ink */
  --color-text: #0a1226;
  --color-text-muted: #4a5568;
  --color-text-faint: #94a0b3;
  --color-text-inverse: #ffffff;

  /* Primary — cobalt blue */
  --color-accent: #0047AB;
  --color-accent-hover: #003585;
  --color-accent-soft: #d6e0f2;

  /* Warm secondary — brick */
  --color-warm: #c15d3c;
  --color-warm-soft: #ecd2c5;

  /* Success + error */
  --color-success: #3d7a41;
  --color-success-soft: #d3e2c9;
  --color-error: #b3324a;
  --color-error-soft: #eccfd3;

  /* Data-viz palette for calculator function colors */
  --f1: #0047AB; /* cobalt */
  --f2: #c15d3c; /* brick */
  --f3: #3d7a41; /* moss */
  --f4: #a13b7f; /* plum */
  --f5: #b78227; /* ochre */
  --f6: #2a6c8a; /* teal-blue */

  /* Shadows */
  --shadow-sm: 0 1px 2px rgba(30, 20, 10, 0.06);
  --shadow-md: 0 4px 14px rgba(30, 20, 10, 0.08);
  --shadow-lg: 0 18px 40px rgba(30, 20, 10, 0.14);

  /* Radii */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-full: 999px;

  /* Type */
  --font-body: 'General Sans', 'Inter', system-ui, sans-serif;
  --font-display: 'Cormorant Garamond', 'Georgia', serif;
  --font-mono: 'JetBrains Mono', ui-monospace, monospace;

  --text-xs: clamp(0.75rem, 0.7rem + 0.2vw, 0.85rem);
  --text-sm: clamp(0.875rem, 0.82rem + 0.25vw, 0.95rem);
  --text-base: clamp(1rem, 0.95rem + 0.25vw, 1.075rem);
  --text-lg: clamp(1.125rem, 1rem + 0.6vw, 1.35rem);
  --text-xl: clamp(1.5rem, 1.2rem + 1.2vw, 2rem);
  --text-2xl: clamp(2rem, 1.4rem + 2.2vw, 3rem);
  --text-hero: clamp(2.5rem, 1.6rem + 4vw, 4.5rem);

  /* Space (4px base) */
  --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;

  --content-narrow: 640px;
  --content-default: 1100px;
  --content-wide: 1280px;

  --transition: 200ms cubic-bezier(0.16, 1, 0.3, 1);
}

[data-theme="dark"] {
  --color-bg: #0a1226;
  --color-surface: #101a33;
  --color-surface-2: #14213f;
  --color-surface-offset: #1a2a4d;
  --color-border: #2d3f66;
  --color-divider: #223256;
  --color-grid: #223256;
  --color-grid-strong: #3a4d76;

  --color-text: #e8ecf3;
  --color-text-muted: #94a3b8;
  --color-text-faint: #56637a;
  --color-text-inverse: #0a1226;

  --color-accent: #4d84e0;
  --color-accent-hover: #6a9aef;
  --color-accent-soft: #1e3563;

  --color-warm: #e9825e;
  --color-warm-soft: #4a2a1e;
  --color-success: #7bbc7f;
  --color-success-soft: #253828;
  --color-error: #e07a8f;
  --color-error-soft: #452028;

  --f1: #4d84e0;
  --f2: #e9825e;
  --f3: #7bbc7f;
  --f4: #d18aba;
  --f5: #e2b761;
  --f6: #6db1cf;

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
  --shadow-md: 0 4px 14px rgba(0, 0, 0, 0.5);
  --shadow-lg: 0 18px 40px rgba(0, 0, 0, 0.6);
}

/* ============================================
   Base
   ============================================ */

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

html {
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  scroll-behavior: smooth;
  scroll-padding-top: 5rem;
}

body {
  min-height: 100dvh;
  line-height: 1.6;
  font-family: var(--font-body);
  font-size: var(--text-base);
  color: var(--color-text);
  background: var(--color-bg);
  background-image:
    linear-gradient(var(--color-grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--color-grid) 1px, transparent 1px);
  background-size: 32px 32px;
  background-position: -1px -1px;
  transition: background-color var(--transition), color var(--transition);
}

body::before {
  /* Subtle vignette */
  content: '';
  position: fixed;
  inset: 0;
  pointer-events: none;
  background: radial-gradient(ellipse at center, transparent 55%, rgba(0, 71, 171, 0.04) 100%);
  z-index: -1;
}

[data-theme="dark"] body::before {
  background: radial-gradient(ellipse at center, transparent 40%, rgba(0, 0, 0, 0.45) 100%);
}

h1, h2, h3, h4 {
  font-family: var(--font-display);
  font-weight: 600;
  line-height: 1.1;
  letter-spacing: -0.01em;
  color: var(--color-text);
}

h1 { font-size: var(--text-hero); }
h2 { font-size: var(--text-2xl); }
h3 { font-size: var(--text-lg); font-weight: 600; }
h4 { font-size: var(--text-base); font-weight: 600; }

p { max-width: 62ch; }

code, .mono {
  font-family: var(--font-mono);
  font-size: 0.9em;
  background: var(--color-surface-offset);
  padding: 0.1em 0.35em;
  border-radius: 4px;
  color: var(--color-accent);
}

[data-theme="dark"] code {
  background: var(--color-surface-offset);
  color: var(--color-accent);
}

a { color: var(--color-accent); text-decoration: none; transition: color var(--transition); }
a:hover { color: var(--color-accent-hover); }

button { cursor: pointer; background: none; border: none; font: inherit; color: inherit; }

img, svg, canvas { display: block; max-width: 100%; }

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

::selection { background: var(--color-accent-soft); color: var(--color-text); }

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}

/* ============================================
   Header
   ============================================ */

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  display: flex;
  align-items: center;
  gap: var(--space-6);
  padding: var(--space-4) clamp(var(--space-4), 4vw, var(--space-8));
  background: color-mix(in oklab, var(--color-surface) 90%, transparent);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-divider);
}

.brand {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  color: var(--color-accent);
  font-weight: 600;
}

.brand-mark { width: 32px; height: 32px; }
.brand-name { font-family: var(--font-display); font-size: 1.25rem; letter-spacing: -0.01em; }

.site-header nav {
  display: flex;
  gap: var(--space-5);
  margin-left: auto;
  margin-right: var(--space-4);
}

.site-header nav a {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  font-weight: 500;
  padding: var(--space-1) var(--space-2);
  border-radius: var(--radius-sm);
}
.site-header nav a:hover { color: var(--color-text); background: var(--color-surface-offset); }

.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px; height: 36px;
  border-radius: var(--radius-sm);
  color: var(--color-text-muted);
  border: 1px solid transparent;
  transition: all var(--transition);
}
.theme-toggle:hover {
  border-color: var(--color-border);
  color: var(--color-text);
  background: var(--color-surface-offset);
}

.nav-toggle {
  display: none;
  align-items: center;
  justify-content: center;
  width: 36px; height: 36px;
  margin-left: var(--space-1);
  border-radius: var(--radius-sm);
  color: var(--color-text-muted);
  border: 1px solid transparent;
  transition: all var(--transition);
}
.nav-toggle:hover {
  border-color: var(--color-border);
  color: var(--color-text);
  background: var(--color-surface-offset);
}

@media (max-width: 720px) {
  .site-header nav {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    flex-direction: column;
    gap: 0;
    margin: 0;
    padding: var(--space-2) var(--space-4) var(--space-4);
    background: var(--color-surface);
    border-bottom: 1px solid var(--color-border);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.04);
    max-height: 0;
    overflow: hidden;
    opacity: 0;
    transition: max-height 0.28s ease, opacity 0.2s ease, padding 0.28s ease;
  }
  .site-header nav.is-open {
    max-height: 400px;
    opacity: 1;
  }
  .site-header nav a {
    padding: var(--space-3) var(--space-2);
    font-size: var(--text-base);
    border-bottom: 1px solid var(--color-border);
    border-radius: 0;
  }
  .site-header nav a:last-child { border-bottom: none; }
  .nav-toggle { display: inline-flex; }
}

/* ============================================
   Sections & layout
   ============================================ */

main { display: flex; flex-direction: column; }

section {
  padding: clamp(var(--space-12), 7vw, var(--space-24)) clamp(var(--space-4), 5vw, var(--space-10));
  max-width: var(--content-wide);
  margin: 0 auto;
  width: 100%;
}

.hero {
  display: grid;
  grid-template-columns: 1.15fr 1fr;
  gap: clamp(var(--space-6), 4vw, var(--space-16));
  align-items: center;
  padding-block: clamp(var(--space-16), 10vw, var(--space-24));
}

@media (max-width: 900px) {
  .hero { grid-template-columns: 1fr; }
}

.eyebrow {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--color-warm);
  margin-bottom: var(--space-4);
}

.hero h1 {
  margin-bottom: var(--space-5);
  text-wrap: balance;
}

.hero .lede {
  font-size: var(--text-lg);
  color: var(--color-text-muted);
  margin-bottom: var(--space-8);
  max-width: 46ch;
  line-height: 1.5;
}

.hero-actions {
  display: flex;
  gap: var(--space-4);
  flex-wrap: wrap;
}

.hero-visual {
  aspect-ratio: 1 / 1;
  max-width: 520px;
  width: 100%;
  justify-self: center;
}

/* ============================================
   Buttons
   ============================================ */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: 0.7em 1.4em;
  border-radius: var(--radius-full);
  font-weight: 500;
  font-size: var(--text-sm);
  border: 1px solid transparent;
  transition: all var(--transition);
  white-space: nowrap;
}

.btn-primary {
  background: var(--color-accent);
  color: var(--color-text-inverse);
}
.btn-primary:hover {
  background: var(--color-accent-hover);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
  color: var(--color-text-inverse);
}

.btn-ghost {
  color: var(--color-text);
  border-color: var(--color-border);
}
.btn-ghost:hover {
  background: var(--color-surface-offset);
  color: var(--color-text);
}

.btn-block { width: 100%; }

.btn-sm { padding: 0.4em 0.9em; font-size: var(--text-xs); }

.btn-warm {
  background: var(--color-warm);
  color: white;
}
.btn-warm:hover { background: color-mix(in oklab, var(--color-warm), black 10%); color: white; }

/* ============================================
   Lesson sections
   ============================================ */

.lesson {
  padding-block: clamp(var(--space-16), 8vw, var(--space-24));
}

.lesson.alt {
  background: var(--color-surface);
  max-width: none;
  padding-inline: 0;
}

.lesson.alt > * {
  max-width: var(--content-wide);
  margin-inline: auto;
  padding-inline: clamp(var(--space-4), 5vw, var(--space-10));
}

.lesson-head {
  margin-bottom: var(--space-12);
  max-width: 780px;
}

.section-number {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.15em;
  color: var(--color-warm);
  margin-bottom: var(--space-3);
}

.lesson-head h2 {
  margin-bottom: var(--space-4);
}

.section-lede {
  font-size: var(--text-lg);
  color: var(--color-text-muted);
  line-height: 1.5;
  max-width: 60ch;
}

.split {
  display: grid;
  grid-template-columns: 1fr 1.1fr;
  gap: clamp(var(--space-6), 4vw, var(--space-12));
  align-items: start;
}

.split.reverse { grid-template-columns: 1.1fr 1fr; }

@media (max-width: 900px) {
  .split, .split.reverse { grid-template-columns: 1fr; }
}

.prose h3 { margin-top: var(--space-6); margin-bottom: var(--space-3); }
.prose h3:first-child { margin-top: 0; }
.prose p { margin-bottom: var(--space-4); color: var(--color-text); }
.prose ul { padding-left: 1.5em; margin-bottom: var(--space-4); }
.prose li { margin-bottom: var(--space-2); }

.equation-block {
  font-family: var(--font-mono);
  font-size: var(--text-lg);
  padding: var(--space-4);
  background: var(--color-surface-offset);
  border-left: 3px solid var(--color-accent);
  border-radius: var(--radius-sm);
  color: var(--color-text) !important;
  max-width: 100%;
}
.equation-block .sub { color: var(--color-text-muted); }

.quadrant-list, .outcome-list {
  list-style: none;
  padding-left: 0;
}
.quadrant-list li, .outcome-list li {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-2) 0;
  border-bottom: 1px dashed var(--color-divider);
}
.quadrant-list li:last-child, .outcome-list li:last-child { border-bottom: none; }

.q-tag {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px; height: 32px;
  border-radius: var(--radius-full);
  background: var(--color-accent-soft);
  color: var(--color-accent);
  font-family: var(--font-mono);
  font-weight: 500;
  font-size: var(--text-sm);
}

.callout {
  margin-top: var(--space-6);
  padding: var(--space-4) var(--space-5);
  background: var(--color-warm-soft);
  border-radius: var(--radius-md);
  border-left: 3px solid var(--color-warm);
  color: var(--color-text);
  font-size: var(--text-sm);
  line-height: 1.55;
}
.callout strong { color: var(--color-warm); font-weight: 600; }

/* ============================================
   Interactive graph card
   ============================================ */

.interactive {
  background: var(--color-surface-2);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-4);
  box-shadow: var(--shadow-sm);
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

.graph-mount {
  width: 100%;
  aspect-ratio: 1 / 1;
  background: var(--color-surface);
  border-radius: var(--radius-md);
  overflow: hidden;
  position: relative;
  touch-action: none;
}

.graph-mount.tall {
  aspect-ratio: 16 / 11;
}

.graph-mount canvas {
  display: block;
  width: 100%;
  height: 100%;
  cursor: crosshair;
}

.readout {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: var(--space-3);
  padding: var(--space-3) var(--space-4);
  background: var(--color-surface-offset);
  border-radius: var(--radius-md);
  font-size: var(--text-sm);
}
.readout > div { display: flex; flex-direction: column; }
.readout .k {
  font-size: var(--text-xs);
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}
.readout .v {
  font-family: var(--font-mono);
  font-weight: 500;
  color: var(--color-text);
  font-size: var(--text-base);
}

.equation-readout .equation {
  font-family: var(--font-mono);
  font-size: var(--text-lg);
  color: var(--color-accent);
  font-weight: 500;
}
.equation-readout .subrise {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--color-text-muted);
  margin-top: var(--space-1);
}

/* ============================================
   Controls (sliders, inputs, family picker)
   ============================================ */

.controls {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
  padding: var(--space-3) var(--space-4);
}

.controls label {
  display: grid;
  grid-template-columns: 130px 1fr auto;
  align-items: center;
  gap: var(--space-3);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

.controls label output {
  font-family: var(--font-mono);
  font-weight: 500;
  color: var(--color-accent);
  min-width: 3ch;
  text-align: right;
}

.controls input[type=range] {
  -webkit-appearance: none;
  appearance: none;
  width: 100%;
  height: 4px;
  background: var(--color-border);
  border-radius: var(--radius-full);
  outline: none;
}

.controls input[type=range]::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 18px; height: 18px;
  background: var(--color-accent);
  border-radius: 50%;
  cursor: pointer;
  transition: transform var(--transition);
}
.controls input[type=range]::-moz-range-thumb {
  width: 18px; height: 18px;
  background: var(--color-accent);
  border-radius: 50%;
  cursor: pointer;
  border: none;
}
.controls input[type=range]:hover::-webkit-slider-thumb { transform: scale(1.15); }

.controls .inline-switch {
  grid-template-columns: auto 1fr;
  font-size: var(--text-sm);
  color: var(--color-text);
}

.controls input[type=checkbox] {
  width: 18px; height: 18px;
  accent-color: var(--color-accent);
}

.family-picker {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-bottom: var(--space-5);
}

.family-picker button {
  padding: var(--space-2) var(--space-4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-full);
  font-size: var(--text-xs);
  font-weight: 500;
  color: var(--color-text-muted);
  transition: all var(--transition);
}

.family-picker button:hover { border-color: var(--color-accent); color: var(--color-accent); }
.family-picker button.active {
  background: var(--color-accent);
  color: var(--color-text-inverse);
  border-color: var(--color-accent);
}

.family-info h4 {
  font-family: var(--font-mono);
  color: var(--color-accent);
  margin-bottom: var(--space-2);
  font-size: var(--text-base);
}

.hidden { display: none !important; }

/* ============================================
   Plotting practice
   ============================================ */

.practice-target {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
  padding: var(--space-4) var(--space-5);
  background: var(--color-accent);
  color: var(--color-text-inverse);
  border-radius: var(--radius-md);
  flex-wrap: wrap;
}

.practice-target .prompt {
  font-family: var(--font-mono);
  font-size: var(--text-lg);
  font-weight: 500;
}
.practice-target .score {
  font-size: var(--text-sm);
  opacity: 0.85;
}

.feedback {
  padding: var(--space-3) var(--space-4);
  border-radius: var(--radius-md);
  font-size: var(--text-sm);
  min-height: 2.75rem;
  display: flex;
  align-items: center;
  gap: var(--space-2);
  background: var(--color-surface-offset);
  color: var(--color-text-muted);
  transition: all var(--transition);
}
.feedback.correct {
  background: var(--color-success-soft);
  color: var(--color-success);
  border-left: 3px solid var(--color-success);
}
.feedback.wrong {
  background: var(--color-error-soft);
  color: var(--color-error);
  border-left: 3px solid var(--color-error);
}

/* ============================================
   Calculator
   ============================================ */

.calculator-section {
  padding-block: clamp(var(--space-16), 8vw, var(--space-24));
}

.calculator {
  display: grid;
  grid-template-columns: 320px 1fr;
  gap: var(--space-6);
  align-items: start;
}

@media (max-width: 900px) {
  .calculator { grid-template-columns: 1fr; }
}

.calc-sidebar {
  background: var(--color-surface-2);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-5);
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

.calc-inputs {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}

.calc-row {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-2) var(--space-3);
  transition: border-color var(--transition);
}

.calc-row:focus-within {
  border-color: var(--color-accent);
  box-shadow: 0 0 0 3px var(--color-accent-soft);
}

.calc-row .swatch {
  width: 14px; height: 14px;
  border-radius: 50%;
  flex-shrink: 0;
}

.calc-row .y-eq {
  font-family: var(--font-mono);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.calc-row input[type=text] {
  flex: 1;
  min-width: 0;
  border: none;
  background: transparent;
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  outline: none;
  color: var(--color-text);
}

.calc-row .remove {
  color: var(--color-text-faint);
  font-size: 1.2em;
  padding: 0 var(--space-1);
}
.calc-row .remove:hover { color: var(--color-error); }

.calc-row.error { border-color: var(--color-error); }
.calc-row.error input { color: var(--color-error); }

.calc-guide h4 {
  font-family: var(--font-body);
  font-size: var(--text-xs);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--color-text-muted);
  margin-top: var(--space-4);
  margin-bottom: var(--space-2);
}

.calc-guide ul {
  list-style: none;
  padding: 0;
  display: grid;
  gap: var(--space-1);
  font-size: var(--text-xs);
  color: var(--color-text-muted);
}
.calc-guide code {
  background: var(--color-surface-offset);
  color: var(--color-accent);
  font-size: 0.85em;
}

.preset-list {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
}
.preset-list button {
  padding: var(--space-1) var(--space-3);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-full);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--color-text-muted);
  transition: all var(--transition);
}
.preset-list button:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
  background: var(--color-surface);
}

.calc-graph-wrap {
  position: relative;
}

.calc-controls {
  position: absolute;
  top: var(--space-3);
  right: var(--space-3);
  display: flex;
  gap: var(--space-2);
  align-items: center;
  background: color-mix(in oklab, var(--color-surface) 92%, transparent);
  padding: var(--space-1) var(--space-2);
  border-radius: var(--radius-full);
  border: 1px solid var(--color-border);
  font-size: var(--text-xs);
}

.calc-controls button {
  width: 28px; height: 28px;
  border-radius: 50%;
  color: var(--color-text-muted);
  font-size: 1.1em;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}
.calc-controls button:hover { background: var(--color-surface-offset); color: var(--color-accent); }

.calc-hint {
  color: var(--color-text-faint);
  padding-inline: var(--space-2);
  font-size: var(--text-xs);
}

@media (max-width: 640px) {
  .calc-hint { display: none; }
}

/* Trace tooltip */
.trace-tip {
  position: absolute;
  background: var(--color-accent);
  color: var(--color-text-inverse);
  padding: var(--space-1) var(--space-2);
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  pointer-events: none;
  transform: translate(-50%, -140%);
  white-space: nowrap;
  box-shadow: var(--shadow-md);
  opacity: 0;
  transition: opacity var(--transition);
}
.trace-tip.show { opacity: 1; }

/* ============================================
   Battleship game
   ============================================ */

.battleship {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-6);
  align-items: start;
}

@media (max-width: 900px) {
  .battleship { grid-template-columns: 1fr; }
}

.battle-board {
  background: var(--color-surface-2);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-4);
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}

.battle-board h3 {
  font-family: var(--font-body);
  font-size: var(--text-sm);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--color-text-muted);
  font-weight: 600;
}

.battle-status {
  padding: var(--space-3);
  border-radius: var(--radius-md);
  background: var(--color-surface-offset);
  font-size: var(--text-sm);
  color: var(--color-text);
  text-align: center;
  min-height: 3em;
  display: flex;
  align-items: center;
  justify-content: center;
}

.battle-status.hit { background: var(--color-warm-soft); color: var(--color-warm); font-weight: 500; }
.battle-status.sunk { background: var(--color-error-soft); color: var(--color-error); font-weight: 600; }
.battle-status.miss { background: var(--color-accent-soft); color: var(--color-accent); }
.battle-status.win { background: var(--color-success-soft); color: var(--color-success); font-weight: 600; }

.battle-input {
  display: flex;
  gap: var(--space-2);
  align-items: center;
  padding: var(--space-3);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
}

.battle-input input {
  flex: 1;
  border: none;
  background: transparent;
  font-family: var(--font-mono);
  font-size: var(--text-base);
  outline: none;
  color: var(--color-text);
  min-width: 0;
}

.battle-input .prefix {
  font-family: var(--font-mono);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.battle-stats {
  display: flex;
  gap: var(--space-4);
  justify-content: space-around;
  padding: var(--space-2);
  border-top: 1px solid var(--color-divider);
  font-size: var(--text-xs);
}
.battle-stats .stat {
  text-align: center;
}
.battle-stats .stat .num {
  font-family: var(--font-mono);
  font-size: var(--text-lg);
  color: var(--color-accent);
  display: block;
  font-weight: 500;
}
.battle-stats .stat .label {
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

/* ============================================
   Close & footer
   ============================================ */

.close {
  text-align: center;
  padding-block: clamp(var(--space-16), 10vw, var(--space-24));
}
.close h2 { margin-bottom: var(--space-4); }
.close p {
  color: var(--color-text-muted);
  font-size: var(--text-lg);
  margin: 0 auto var(--space-8);
  max-width: 55ch;
}

.coming-soon {
  padding-block: var(--space-16);
  border-top: 1px solid var(--color-divider);
}

.coming-soon .grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: var(--space-4);
  margin-top: var(--space-6);
}

.coming-soon .card {
  padding: var(--space-5);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  opacity: 0.75;
}

.coming-soon .card h4 { margin-bottom: var(--space-2); font-family: var(--font-body); }
.coming-soon .card p {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  margin: 0;
}
.coming-soon .card .badge {
  display: inline-block;
  padding: 2px 8px;
  background: var(--color-accent-soft);
  color: var(--color-accent);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  border-radius: var(--radius-full);
  margin-bottom: var(--space-3);
}

footer {
  padding: var(--space-8);
  text-align: center;
  font-size: var(--text-xs);
  color: var(--color-text-faint);
  border-top: 1px solid var(--color-divider);
}

/* ============================================
   Number line & Timeline section (01)
   ============================================ */

.numline-mount {
  position: relative;
  width: 100%;
  height: 220px;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 6px;
  overflow: hidden;
  touch-action: none;
  user-select: none;
}

.timeline-mount {
  position: relative;
  width: 100%;
  height: 260px;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 6px;
  overflow: hidden;
  touch-action: none;
  user-select: none;
}

.nl-controls {
  display: flex;
  gap: 8px;
  margin-top: 12px;
  flex-wrap: wrap;
}

.chip {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  letter-spacing: 0.03em;
  text-transform: uppercase;
  padding: 6px 12px;
  border-radius: 999px;
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  color: var(--color-text-muted);
  cursor: pointer;
  transition: all 160ms ease;
}
.chip:hover {
  border-color: var(--color-accent);
  color: var(--color-text);
}
.chip.is-active {
  background: var(--color-accent);
  color: var(--color-text-inverse);
  border-color: var(--color-accent);
}

/* Give the second split (timeline) extra top spacing */
.split-timeline {
  margin-top: 72px;
  padding-top: 48px;
  border-top: 1px dashed var(--color-divider);
}

@media (max-width: 720px) {
  .numline-mount { height: 180px; }
  .timeline-mount { height: 220px; }
  .split-timeline { margin-top: 48px; padding-top: 32px; }
}

/* ============================================
   Site footer (expanded)
   ============================================ */

.site-footer {
  margin-top: 96px;
  padding: 64px 0 32px;
  background: var(--color-surface-offset);
  border-top: 1px solid var(--color-divider);
  color: var(--color-text-muted);
}

.footer-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 32px;
  display: grid;
  grid-template-columns: 1.2fr 3fr;
  gap: 64px;
  align-items: start;
}

.footer-brand {
  display: flex;
  gap: 14px;
  align-items: flex-start;
  color: var(--color-accent);
}

.footer-brand svg { flex-shrink: 0; margin-top: 2px; }

.footer-name {
  font-family: var(--font-display, "Cormorant Garamond", Georgia, serif);
  font-size: 20px;
  font-weight: 600;
  color: var(--color-text);
  margin: 0;
}

.footer-tagline {
  font-size: 14px;
  color: var(--color-text-muted);
  margin: 4px 0 0;
  line-height: 1.5;
}

.footer-nav {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 32px;
}

.footer-col { display: flex; flex-direction: column; gap: 10px; }

.footer-heading {
  font-family: var(--font-mono, "JetBrains Mono", monospace);
  font-size: 11px;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-text-faint);
  margin: 0 0 4px;
}

.footer-col a {
  color: var(--color-text-muted);
  text-decoration: none;
  font-size: 14px;
  transition: color 0.15s;
}

.footer-col a:hover { color: var(--color-accent); }

.footer-bottom {
  max-width: 1200px;
  margin: 48px auto 0;
  padding: 24px 32px 0;
  border-top: 1px solid var(--color-divider);
  display: flex;
  justify-content: space-between;
  gap: 16px;
  font-size: 13px;
  color: var(--color-text-faint);
}

.footer-bottom p { margin: 0; }

@media (max-width: 720px) {
  .footer-inner {
    grid-template-columns: 1fr;
    gap: 40px;
    padding: 0 20px;
  }
  .footer-nav {
    grid-template-columns: repeat(2, 1fr);
    gap: 24px;
  }
  .footer-bottom {
    flex-direction: column;
    padding: 20px 20px 0;
    text-align: left;
  }
}

/* ============================================
   Subpage layout (about / contact / privacy / terms / 404)
   ============================================ */

.page {
  max-width: 780px;
  margin: 0 auto;
  padding: 96px 32px 48px;
}

.page-head {
  margin-bottom: 64px;
  padding-bottom: 32px;
  border-bottom: 1px solid var(--color-divider);
}

.page-head .eyebrow {
  font-family: var(--font-mono, "JetBrains Mono", monospace);
  font-size: 12px;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-warm);
  margin: 0 0 20px;
}

.page-head h1 {
  font-family: var(--font-display, "Cormorant Garamond", Georgia, serif);
  font-size: clamp(38px, 5vw, 56px);
  font-weight: 700;
  line-height: 1.05;
  letter-spacing: -0.01em;
  margin: 0 0 24px;
  color: var(--color-text);
}

.page-head .lede {
  font-size: 19px;
  line-height: 1.55;
  color: var(--color-text-muted);
  margin: 0;
  max-width: 640px;
}

.page-body {
  font-size: 17px;
  line-height: 1.7;
  color: var(--color-text);
}

.page-body h2 {
  font-family: var(--font-display, "Cormorant Garamond", Georgia, serif);
  font-size: 28px;
  font-weight: 600;
  margin: 48px 0 16px;
  color: var(--color-text);
}

.page-body h2:first-child { margin-top: 0; }

.page-body h3 {
  font-size: 18px;
  font-weight: 600;
  margin: 32px 0 8px;
  color: var(--color-text);
}

.page-body p { margin: 0 0 16px; }

.page-body ul {
  margin: 0 0 16px;
  padding-left: 24px;
}

.page-body ul li { margin-bottom: 8px; }

.page-body a:not(.btn):not(.notfound-card) {
  color: var(--color-accent);
  text-decoration: underline;
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
}

.page-body a:not(.btn):not(.notfound-card):hover { color: var(--color-warm); }

.page-body em { font-style: italic; color: var(--color-text-muted); }
.page-body strong { font-weight: 600; }

.cta-block {
  margin-top: 64px;
  padding: 40px;
  background: var(--color-surface);
  border: 1px solid var(--color-divider);
  border-radius: 12px;
  text-align: center;
}

.cta-block .cta-heading {
  font-family: var(--font-display, "Cormorant Garamond", Georgia, serif);
  font-size: 24px;
  font-weight: 600;
  color: var(--color-text);
  margin: 0 0 24px;
}

.cta-actions {
  display: flex;
  gap: 12px;
  justify-content: center;
  flex-wrap: wrap;
}

/* Contact page */
.contact-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 24px;
  margin-top: 24px;
}

.contact-card {
  padding: 28px;
  background: var(--color-surface);
  border: 1px solid var(--color-divider);
  border-radius: 12px;
}

.contact-card h3 {
  font-family: var(--font-display, "Cormorant Garamond", Georgia, serif);
  font-size: 20px;
  font-weight: 600;
  margin: 0 0 10px;
  color: var(--color-text);
}

.contact-card p { font-size: 15px; margin: 0 0 10px; color: var(--color-text-muted); }
.contact-card p:last-child { margin-bottom: 0; }

.contact-link {
  font-family: var(--font-mono, "JetBrains Mono", monospace);
  font-size: 14px;
  color: var(--color-warm) !important;
}

/* 404 page */
.notfound-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 16px;
  margin-top: 24px;
}

.notfound-card {
  padding: 24px;
  background: var(--color-surface);
  border: 1px solid var(--color-divider);
  border-radius: 12px;
  text-decoration: none !important;
  transition: border-color 0.15s, transform 0.15s;
}

.notfound-card:hover {
  border-color: var(--color-accent);
  transform: translateY(-2px);
}

.notfound-title {
  font-family: var(--font-display, "Cormorant Garamond", Georgia, serif);
  font-size: 20px;
  font-weight: 600;
  margin: 0 0 8px;
  color: var(--color-text) !important;
}

.notfound-desc {
  font-size: 14px;
  line-height: 1.5;
  color: var(--color-text-muted);
  margin: 0;
}

@media (max-width: 720px) {
  .page { padding: 48px 20px 32px; }
  .page-head { margin-bottom: 40px; padding-bottom: 24px; }
  .page-head h1 { font-size: 36px; }
  .page-head .lede { font-size: 17px; }
  .page-body { font-size: 16px; }
  .page-body h2 { font-size: 24px; margin-top: 36px; }
  .contact-grid, .notfound-grid { grid-template-columns: 1fr; }
  .cta-block { padding: 28px 20px; }
}