/* Shared dark theme for the First-Order ODE animated lessons
   Matches the portfolio hub pages (ode/, hopfield/): #120a12 background,
   glass cards, teal / pink / wine / purple accents. */

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

:root {
  --bg: #120a12;
  --text: #e5e7eb;
  --muted: #9aa6b2;
  --panel: rgba(17, 24, 39, 0.55);
  --border: rgba(255, 255, 255, 0.1);
  --teal: #2dd4d4;
  --pink: #ff4db8;
  --wine: #ff5a7a;
  --purple: #a78bfa;
  --amber: #fbbf24;
  --green: #34d399;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Inter', 'Segoe UI', sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  overflow-x: hidden;
  line-height: 1.65;
}

body::after {
  content: '';
  position: fixed;
  inset: 0;
  background: radial-gradient(ellipse at center, rgba(22, 153, 153, 0.04) 0%, transparent 70%);
  z-index: 0;
  pointer-events: none;
}

.container {
  position: relative;
  z-index: 1;
  max-width: 1000px;
  margin: 0 auto;
  padding: 0 32px 40px;
}

nav {
  padding: 26px 0 10px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
}

.back-link {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.95rem;
  transition: color 0.2s;
  white-space: nowrap;
}

.back-link:hover { color: #ffffff; }

.page-tag {
  font-size: 0.85rem;
  color: var(--muted);
  letter-spacing: 0.02em;
}

h1 {
  font-size: 2rem;
  font-weight: 650;
  letter-spacing: -0.02em;
  margin: 18px 0 6px;
  line-height: 1.25;
}

.accent-bar {
  width: 64px;
  height: 4px;
  border-radius: 2px;
  margin: 10px 0 26px;
}

.theme-teal .accent-bar { background: linear-gradient(90deg, #169999, #2dd4d4); }
.theme-pink .accent-bar { background: linear-gradient(90deg, #c2308f, #ff4db8); }
.theme-wine .accent-bar { background: linear-gradient(90deg, #990f23, #ff5a7a); }
.theme-purple .accent-bar { background: linear-gradient(90deg, #6d4fd8, #a78bfa); }

section.card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 16px;
  backdrop-filter: blur(8px);
  padding: 26px 28px;
  margin-bottom: 26px;
}

section.card h2 {
  font-size: 1.3rem;
  font-weight: 600;
  margin-bottom: 12px;
  letter-spacing: -0.01em;
}

section.card p { margin-bottom: 14px; }
section.card p:last-child { margin-bottom: 0; }

.eq {
  text-align: center;
  margin: 16px 0;
  overflow-x: auto;
  overflow-y: hidden;
  padding: 2px 0;
}

/* two-column: text + animation panel */
.split {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 26px;
  align-items: center;
}

.panel {
  background: rgba(10, 8, 16, 0.55);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 12px;
  margin: 6px 0;
}

.panel canvas {
  display: block;
  width: 100%;
  aspect-ratio: 4 / 3;
  cursor: pointer;
}

.panel canvas.square { aspect-ratio: 1 / 1; }
.panel canvas.wide { aspect-ratio: 16 / 9; }

.panel figcaption {
  text-align: center;
  font-size: 0.85rem;
  color: var(--muted);
  padding-top: 8px;
}

.note {
  border-left: 3px solid var(--teal);
  background: rgba(22, 153, 153, 0.08);
  border-radius: 0 10px 10px 0;
  padding: 14px 18px;
  margin: 16px 0;
}

.note.pink   { border-left-color: var(--pink);   background: rgba(255, 77, 184, 0.07); }
.note.wine   { border-left-color: var(--wine);   background: rgba(153, 15, 35, 0.14); }
.note.purple { border-left-color: var(--purple); background: rgba(139, 92, 246, 0.09); }
.note.amber  { border-left-color: var(--amber);  background: rgba(251, 191, 36, 0.07); }
.note.green  { border-left-color: var(--green);  background: rgba(52, 211, 153, 0.08); }

.note .note-title { font-weight: 650; margin-bottom: 6px; }

table.classify {
  width: 100%;
  border-collapse: collapse;
  margin: 16px 0;
  font-size: 0.95rem;
}

table.classify th, table.classify td {
  border: 1px solid var(--border);
  padding: 10px 12px;
  text-align: left;
  vertical-align: top;
}

table.classify th {
  background: rgba(255, 255, 255, 0.05);
  font-weight: 600;
}

.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin: 8px 0 20px;
}

.lesson-nav a {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.92rem;
  transition: color 0.2s;
}

.lesson-nav a:hover { color: #ffffff; }

.footer {
  text-align: center;
  padding: 24px 20px 8px;
  font-size: 0.8rem;
  color: rgba(255, 255, 255, 0.5);
}

@media (max-width: 760px) {
  .container { padding: 0 18px 30px; }

  /* 2026-09-03. `1fr` IS `minmax(auto, 1fr)`, AND `auto` FLOORS AT MIN-CONTENT.
     Stacking .split to one column was already right and was not enough: a grid track's
     automatic minimum is the min-content width of its widest item, and a long unbreakable
     equation has a large one. On example-3.html the single column measured 424px inside a
     316px box, so the page was 461px wide at a 390px viewport.

     AND IT DID NOT SCROLL. `body { overflow-x: hidden }` clips instead, so those 71px were
     not off to the side -- they were unreachable. Verified by scrolling: window.scrollTo(300,0)
     left scrollX at 0. A reader on a phone simply could not see part of the formula.

     minmax(0, 1fr) removes the min-content floor; the equation then scrolls inside its own
     box rather than pushing the page. Measured across four lesson pages: example-3 461 -> 390,
     singularity-definitions 413 -> 390 (its table), introduction and stitching-solutions
     unchanged at 390. Page heights moved by at most 3px, so nothing reflowed into a
     cramped stack, and before/after screenshots at the same scroll position are identical. */
  .split { grid-template-columns: minmax(0, 1fr); }
  mjx-container { display: inline-block; max-width: 100%;
                  overflow-x: auto; overflow-y: hidden; vertical-align: middle; }
  table { display: block; overflow-x: auto; max-width: 100%; }

  h1 { font-size: 1.5rem; }
  section.card { padding: 20px 18px; }
}