: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: 1.08rem; }
li { margin-bottom: 0.5rem; }
.explanation-list { padding-left: 1.5rem; margin: 1rem 0; }
.math-block { margin: 1.4rem 0; padding: 0.6rem 0.8rem; overflow-x: auto; background: rgba(0,0,0,0.02); border-radius: 12px; text-align: center; }

.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: 150px; accent-color: var(--accent); }
.train-controls select { font: 600 0.88rem var(--sans); padding: 0.4rem 0.6rem; border: 1px solid var(--border); border-radius: 8px; background: white; }
.train-stat { color: var(--muted); font-size: 0.92rem; }
.train-stat strong { color: var(--text); font-family: var(--mono); }

.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--warn { border-left-color: #b86b2a; background: rgba(184,107,42,0.05); }
.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; }
}

/* ===== Live playground (Step 5) ===== */
.pm-stage {
  display: grid; grid-template-columns: 1fr 1fr; gap: 1rem;
  margin: 1rem 0;
}
@media (max-width: 720px) { .pm-stage { grid-template-columns: 1fr; } }
.pm-panel {
  background: white; border: 1px solid var(--border);
  border-radius: 14px; padding: 0.75rem 0.85rem 0.9rem;
  display: flex; flex-direction: column; align-items: center; gap: 0.45rem;
}
.pm-panel canvas { width: 256px; height: 256px; image-rendering: pixelated; border-radius: 8px; background: #fafaf6; border: 1px solid var(--border); }
.panel-label { font-family: var(--sans); font-weight: 600; font-size: 0.86rem; color: var(--text); }
.panel-sub { font-family: var(--mono); font-size: 0.72rem; color: var(--muted); }

.pm-metrics {
  display: grid; grid-template-columns: repeat(4, 1fr); gap: 0.6rem;
  margin: 0.8rem 0 0.4rem;
  font-family: var(--sans);
}
@media (max-width: 720px) { .pm-metrics { grid-template-columns: repeat(2, 1fr); } }
.metric-card {
  background: rgba(44, 111, 183, 0.05);
  border: 1px solid rgba(44, 111, 183, 0.18);
  border-radius: 10px;
  padding: 0.55rem 0.7rem;
  display: flex; flex-direction: column; gap: 0.15rem;
}
.metric-card .m-label { font-size: 0.78rem; color: var(--muted); text-transform: uppercase; letter-spacing: 0.05em; }
.metric-card .m-value { font-family: var(--mono); font-size: 1.15rem; color: var(--text); font-weight: 600; }
.metric-card .m-hint { font-size: 0.72rem; color: var(--muted); font-style: italic; }
.metric-card.is-good { background: rgba(30,119,112,0.07); border-color: rgba(30,119,112,0.25); }
.metric-card.is-warn { background: rgba(184,107,42,0.08); border-color: rgba(184,107,42,0.25); }
.metric-card.is-bad  { background: rgba(217,98,43,0.10); border-color: rgba(217,98,43,0.28); }

.pm-controls {
  display: grid;
  grid-template-columns: 220px 1fr 80px;
  gap: 0.7rem;
  align-items: center;
  font-family: var(--sans);
  margin-top: 0.5rem;
}
@media (max-width: 640px) { .pm-controls { grid-template-columns: 1fr; } }
.pm-controls .ctrl-label { font-size: 0.92rem; color: var(--text); }
.pm-controls .ctrl-num { font-family: var(--mono); font-size: 0.85rem; color: var(--muted); text-align: right; }
.pm-controls input[type=range] { accent-color: var(--accent); width: 100%; }

/* ===== Equal-PSNR gallery (Step 6) ===== */
.pm-gallery {
  display: grid; grid-template-columns: repeat(6, 1fr); gap: 0.6rem;
  margin: 1rem 0;
}
@media (max-width: 980px) { .pm-gallery { grid-template-columns: repeat(3, 1fr); } }
@media (max-width: 560px) { .pm-gallery { grid-template-columns: repeat(2, 1fr); } }

.pm-card {
  background: white; border: 1px solid var(--border);
  border-radius: 12px; padding: 0.55rem 0.6rem 0.7rem;
  display: flex; flex-direction: column; gap: 0.35rem; align-items: center;
}
.pm-card canvas { width: 100%; aspect-ratio: 1/1; image-rendering: pixelated; border-radius: 6px; background: #fafaf6; border: 1px solid var(--border); }
.pm-card .panel-label { font-size: 0.78rem; text-align: center; }
.pm-card .pm-card-stats { display: flex; flex-direction: column; gap: 0.15rem; align-items: center; font-family: var(--mono); font-size: 0.7rem; color: var(--muted); }
.pm-card .pm-card-stats strong { color: var(--text); font-weight: 600; }

/* Decision table */
.pm-table {
  width: 100%;
  border-collapse: collapse;
  margin: 1rem 0;
  font-family: var(--sans);
  font-size: 0.92rem;
}
.pm-table th, .pm-table td { border: 1px solid var(--border); padding: 0.55rem 0.7rem; text-align: left; vertical-align: top; }
.pm-table th { background: rgba(44, 111, 183, 0.06); font-weight: 600; color: var(--text); }
.pm-table td code { font-family: var(--mono); font-size: 0.85rem; background: rgba(0,0,0,0.04); padding: 0.1rem 0.35rem; border-radius: 4px; }