:root {
  --serif: 'Source Serif 4', Georgia, serif;
  --sans: 'Manrope', -apple-system, BlinkMacSystemFont, sans-serif;
  --mono: 'IBM Plex Mono', monospace;
  --bg: #fdfcf9; --paper: #ffffff; --text: #2f2a22; --muted: #6e665b;
  --border: #e2d8c6; --accent: #2c6fb7; --accent-hover: #1e528a;
}
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { margin: 0; font-family: var(--serif); color: var(--text); background: var(--bg); line-height: 1.65; }
.article { max-width: 980px; margin: 0 auto; padding: 2.5rem 1.5rem 5rem; }
.back-link { display: inline-block; margin-bottom: 1.5rem; color: var(--muted); text-decoration: none; font-family: var(--sans); font-size: 0.9rem; }
.back-link:hover { color: var(--text); }
.article-header { margin-bottom: 3rem; text-align: center; }
.kicker { margin: 0 0 0.75rem; font-family: var(--sans); font-size: 0.8rem; text-transform: uppercase; letter-spacing: 0.14em; color: var(--muted); }
h1 { margin: 0 auto 1rem; font-size: clamp(2.4rem, 5vw, 3.5rem); line-height: 1.1; letter-spacing: -0.02em; color: #1a1815; max-width: 18ch; }
.abstract { margin: 0 auto 1rem; max-width: 64ch; font-size: 1.15rem; color: #4d463d; }
.byline { display: flex; gap: 1rem; justify-content: center; flex-wrap: wrap; margin-top: 1.4rem; padding-top: 1rem; border-top: 1px solid var(--border); color: var(--muted); font-family: var(--sans); font-size: 0.92rem; }

.step-section {
  position: relative; margin-top: 4rem; padding: 3rem 2.5rem;
  background: var(--paper); border: 1px solid var(--border);
  border-radius: 24px; box-shadow: 0 8px 30px rgba(0, 0, 0, 0.03);
}
.step-badge {
  position: absolute; top: -16px; left: 32px;
  background: var(--accent); color: white;
  font-family: var(--sans); font-weight: 700; font-size: 0.85rem;
  text-transform: uppercase; letter-spacing: 0.08em;
  padding: 0.4rem 1.2rem; border-radius: 999px;
  box-shadow: 0 4px 12px rgba(44, 111, 183, 0.25);
}
h2 { margin: 0 0 1rem; font-size: clamp(1.6rem, 3.5vw, 2.2rem); line-height: 1.15; color: #1a1815; }
p, ul { max-width: 68ch; font-size: 1.1rem; }
li { margin-bottom: 0.5rem; }
.explanation-list { padding-left: 1.5rem; margin: 1rem 0; }
.math-block { margin: 1.5rem 0; padding: 0.6rem 0.8rem; overflow-x: auto; background: rgba(0,0,0,0.02); border-radius: 12px; text-align: center; }

.action-btn {
  border: 1px solid var(--accent); background: var(--accent); color: white;
  padding: 0.55rem 1rem; border-radius: 999px;
  font: 600 0.88rem var(--sans); cursor: pointer;
}
.action-btn:hover { background: var(--accent-hover); }
.action-btn--ghost { background: white; color: var(--text); border-color: var(--border); }
.action-btn--ghost:hover { border-color: var(--accent); }

.train-controls {
  display: flex; align-items: center; gap: 0.9rem; flex-wrap: wrap;
  margin: 0.8rem 0 1.2rem;
  font-family: var(--sans); color: var(--text);
}
.train-controls label { display: flex; align-items: center; gap: 0.5rem; font-size: 0.92rem; }
.train-controls input[type=range] { width: 130px; accent-color: var(--accent); }
.train-stat { color: var(--muted); font-size: 0.92rem; }
.train-stat strong { color: var(--text); font-family: var(--mono); }

.cal-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1rem; margin: 1rem 0; }
@media (max-width: 880px) { .cal-grid { grid-template-columns: 1fr; } }
.cal-panel {
  background: white; border: 1px solid var(--border);
  border-radius: 14px; padding: 0.8rem 0.9rem 1rem;
  display: flex; flex-direction: column; gap: 0.4rem; align-items: center;
}
.cal-panel canvas { width: 100%; height: auto; display: block; border-radius: 8px; background: #fdfcf9; }
.panel-label { font-family: var(--sans); font-weight: 600; font-size: 0.86rem; color: var(--text); }

.callout {
  margin: 1.6rem 0; padding: 1.1rem 1.3rem;
  border-left: 4px solid var(--accent);
  background: rgba(44, 111, 183, 0.04);
  border-radius: 0 12px 12px 0; font-size: 1rem;
}
.callout strong { font-family: var(--sans); font-size: 0.9rem; }
.callout--think { border-left-color: #d9622b; background: rgba(217,98,43,0.04); }
.callout--key   { border-left-color: #1e7770; background: rgba(30,119,112,0.05); }

@media (max-width: 640px) {
  .article { padding-inline: 1rem; }
  .step-section { padding: 2rem 1.5rem; }
}

.cal-multi-figure {
  margin: 1.4rem 0; padding: 1.1rem;
  background: white; border: 1px solid var(--border); border-radius: 16px;
}
.cal-multi-figure canvas { width: 100%; height: auto; display: block; border-radius: 8px; background: #fdfcf9; }
.cal-multi-figure figcaption { margin-top: 0.6rem; text-align: center; font-family: var(--sans); font-size: 0.92rem; color: var(--muted); }

.dt-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1rem; margin: 1rem 0; }
@media (max-width: 880px) { .dt-grid { grid-template-columns: 1fr; } }
.dt-panel {
  background: white; border: 1px solid var(--border);
  border-radius: 14px; padding: 0.8rem 0.9rem 1rem;
  display: flex; flex-direction: column; gap: 0.4rem; align-items: center;
}
.dt-panel canvas { width: 100%; height: auto; display: block; border-radius: 8px; background: #fdfcf9; cursor: crosshair; }
.train-controls select { font: 600 0.88rem var(--sans); padding: 0.4rem 0.6rem; border: 1px solid var(--border); border-radius: 8px; background: white; }

.xg-figure { margin: 1rem 0; padding: 1rem; background: white; border: 1px solid var(--border); border-radius: 14px; }
.xg-figure canvas { width: 100%; height: auto; display: block; border-radius: 8px; background: #fdfcf9; }
.xg-figure figcaption { margin-top: 0.5rem; text-align: center; font-family: var(--sans); font-size: 0.88rem; color: var(--muted); }