:root {
  --bg: #f5f7fb;
  --card: #ffffff;
  --ink: #1c2433;
  --muted: #5a6478;
  --accent: #4f46e5;
  --accent-2: #06b6d4;
  --good: #16a34a;
  --bad: #dc2626;
  --border: #e3e7ef;
  --shadow: 0 6px 20px rgba(20, 30, 60, 0.06);
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  line-height: 1.55;
  font-size: 16px;
}

.container {
  max-width: 1080px;
  margin: 0 auto;
  padding: 0 24px;
}

/* ===== HERO ===== */
.hero {
  background: linear-gradient(135deg, #4f46e5 0%, #06b6d4 100%);
  color: white;
  padding: 56px 0 40px;
}
.hero .eyebrow {
  text-transform: uppercase;
  letter-spacing: 1.5px;
  font-size: 13px;
  opacity: 0.85;
  margin: 0 0 8px;
}
.hero h1 {
  font-size: clamp(34px, 5vw, 52px);
  margin: 0 0 12px;
  font-weight: 800;
}
.hero .lede {
  font-size: 18px;
  max-width: 680px;
  opacity: 0.95;
  margin: 0 0 24px;
}
.toc {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 16px;
}
.toc a {
  background: rgba(255,255,255,0.18);
  color: white;
  text-decoration: none;
  padding: 8px 14px;
  border-radius: 999px;
  font-size: 14px;
  transition: background 0.2s;
}
.toc a:hover { background: rgba(255,255,255,0.32); }

/* ===== CARDS / SECTIONS ===== */
.card {
  background: var(--card);
  margin: 28px 0;
  padding: 32px;
  border-radius: 16px;
  box-shadow: var(--shadow);
  border: 1px solid var(--border);
}
.card h2 {
  font-size: 26px;
  margin: 0 0 18px;
  display: flex;
  align-items: center;
  gap: 12px;
}
.card h2 .num {
  display: inline-grid;
  place-items: center;
  width: 36px; height: 36px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: white;
  font-size: 16px;
  font-weight: 700;
}
.card h3 {
  margin-top: 28px;
  font-size: 19px;
}

.two-col {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 28px;
  align-items: center;
}
@media (max-width: 720px) {
  .two-col { grid-template-columns: 1fr; }
}

.callout {
  background: #eef2ff;
  border-left: 4px solid var(--accent);
  padding: 14px 18px;
  border-radius: 8px;
  margin: 18px 0;
}

code {
  background: #f1f3f9;
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.9em;
  font-family: "SF Mono", Menlo, Consolas, monospace;
}

/* ===== CANVAS / FIGURES ===== */
figure {
  margin: 0;
  text-align: center;
}
canvas {
  background: #f1f3f9;
  border-radius: 10px;
  border: 1px solid var(--border);
  image-rendering: pixelated;
  max-width: 100%;
  height: auto;
}
figcaption {
  margin-top: 8px;
  color: var(--muted);
  font-size: 14px;
}
.mosaic-demo canvas { background: white; }

/* ===== CONTROLS ===== */
.controls {
  margin-top: 16px;
}
.controls.wide { margin-top: 20px; }
.controls label {
  font-weight: 600;
  display: block;
  margin-bottom: 8px;
}
.controls output {
  font-weight: 700;
  color: var(--accent);
  margin-left: 6px;
}
.controls input[type="range"] {
  width: 100%;
  accent-color: var(--accent);
}
.hint {
  color: var(--muted);
  font-size: 14px;
  margin: 8px 0 0;
}

/* ===== ZOOM DEMO ===== */
.zoom-demo {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 28px;
  align-items: center;
  margin-top: 12px;
}
@media (max-width: 720px) {
  .zoom-demo { grid-template-columns: 1fr; }
}
.zoom-stage {
  text-align: center;
}

/* ===== PIXEL ART ===== */
.pixel-art {
  margin-top: 14px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
}
.palette {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  justify-content: center;
}
.swatch {
  width: 32px;
  height: 32px;
  border-radius: 6px;
  border: 2px solid transparent;
  cursor: pointer;
  font-size: 16px;
  color: #555;
}
.swatch.active {
  border-color: var(--ink);
  transform: scale(1.1);
}
#pixelArt {
  cursor: crosshair;
  background: white;
}

/* ===== BUTTONS ===== */
.btn {
  background: var(--accent);
  color: white;
  border: none;
  padding: 10px 20px;
  border-radius: 8px;
  font-size: 15px;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s;
}
.btn:hover { background: #3730a3; }

/* ===== TABLE ===== */
.depth-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
  margin: 12px 0;
}
.depth-table th, .depth-table td {
  text-align: left;
  padding: 8px 10px;
  border-bottom: 1px solid var(--border);
}
.depth-table th {
  background: #f7f9fc;
  font-weight: 700;
}

/* ===== COLOUR/BINARY TABLE ===== */
.colour-binary-table {
  width: 100%;
  border-collapse: collapse;
  margin: 14px 0;
  font-size: 15px;
  max-width: 520px;
}
.colour-binary-table th, .colour-binary-table td {
  padding: 8px 12px;
  border-bottom: 1px solid var(--border);
  text-align: left;
}
.colour-binary-table th {
  background: #f7f9fc;
  font-weight: 700;
  font-size: 14px;
}
.colour-binary-table code {
  font-size: 15px;
  letter-spacing: 1px;
}
.swatch-box {
  display: inline-block;
  width: 32px;
  height: 24px;
  border-radius: 4px;
  vertical-align: middle;
}

/* ===== FILE SIZE / CALC ===== */
.formula {
  background: #1c2433;
  color: #f1f3f9;
  padding: 18px;
  border-radius: 10px;
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: 17px;
  text-align: center;
  margin: 14px 0;
}
.calc {
  background: #f7f9fc;
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px;
  margin-top: 16px;
}
.calc-inputs {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 14px;
}
@media (max-width: 600px) {
  .calc-inputs { grid-template-columns: 1fr; }
}
.calc-inputs label {
  display: flex;
  flex-direction: column;
  font-weight: 600;
  font-size: 14px;
  gap: 4px;
}
.calc-inputs input, .calc-inputs select {
  padding: 8px 10px;
  border: 1px solid var(--border);
  border-radius: 6px;
  font-size: 15px;
  font-family: inherit;
  background: white;
}
.calc-output {
  margin-top: 16px;
  padding: 14px;
  background: white;
  border-radius: 8px;
  font-size: 15px;
  border: 1px dashed var(--border);
}
.calc-output strong { color: var(--accent); }

/* ===== CHALLENGES ===== */
.challenge {
  margin-top: 22px;
  padding: 20px;
  background: #fef9f3;
  border-radius: 12px;
  border-left: 4px solid #f59e0b;
}
.challenge h3 { margin-top: 0; }
.challenge-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 24px;
  margin-top: 12px;
}
@media (max-width: 600px) {
  .challenge-grid { grid-template-columns: 1fr; }
}
.challenge-grid figure label {
  display: block;
  margin-top: 8px;
  font-size: 13px;
  font-weight: 600;
}
.challenge-grid figure input[type=range] {
  width: 100%;
  accent-color: #f59e0b;
}

/* ===== QUIZ ===== */
.quiz ol { padding-left: 22px; }
.quiz li { margin-bottom: 18px; }
.quiz label {
  display: block;
  padding: 8px 12px;
  margin: 4px 0;
  border-radius: 6px;
  cursor: pointer;
  transition: background 0.15s;
}
.quiz label:hover { background: #eef2ff; }
.quiz-result {
  margin-top: 16px;
  font-size: 17px;
  font-weight: 600;
}
.quiz-result.good { color: var(--good); }
.quiz-result.bad  { color: var(--bad); }

/* ===== SUMMARY ===== */
.summary {
  background: linear-gradient(135deg, #eef2ff 0%, #ecfeff 100%);
}
.summary ul { padding-left: 22px; line-height: 1.8; }

/* ===== FOOTER ===== */
footer {
  padding: 30px 0 40px;
  color: var(--muted);
  font-size: 14px;
  text-align: center;
}