/* ═══════════════════════════════════════════════════════════════
   ML Portal — Design System
   A shared style foundation for all portal collections.
   ═══════════════════════════════════════════════════════════════ */

@import url('https://fonts.googleapis.com/css2?family=IBM+Plex+Mono:ital,wght@0,300;0,400;0,500;1,300&family=Playfair+Display:ital,wght@0,400;0,700;1,400&family=Inter:wght@300;400;500;600;700&display=swap');

/* ── Tokens ── */
:root {
  --bg:       #faf8f4;
  --surface:  #ffffff;
  --surface2: #f2ede4;
  --border:   #e2d9cc;
  --border2:  #c9bead;
  --accent:   #c84b2f;
  --accent2:  #2a7d5f;
  --accent3:  #2955a0;
  --accent4:  #8b4fa8;
  --text:     #1a1714;
  --muted:    #7a6e62;
  --hi:       rgba(200,75,47,0.06);
  --nav-w:    260px;
  --hdr-h:    64px;
  --radius:   10px;
  --shadow-sm: 0 1px 3px rgba(0,0,0,.06);
  --shadow-md: 0 4px 20px rgba(0,0,0,.08);
  --shadow-lg: 0 12px 40px rgba(0,0,0,.12);
  --mono:     'IBM Plex Mono', monospace;
  --serif:    'Playfair Display', Georgia, serif;
  --sans:     'Inter', -apple-system, sans-serif;
  --ease:     cubic-bezier(.4,0,.2,1);
}

/* ── Dark mode ── */
@media (prefers-color-scheme: dark) {
  :root {
    --bg:       #141210;
    --surface:  #1c1a17;
    --surface2: #242119;
    --border:   #332e27;
    --border2:  #4a4237;
    --text:     #e8e2d8;
    --muted:    #9a8e80;
    --hi:       rgba(200,75,47,0.1);
  }
}
[data-theme="dark"] {
  --bg:       #141210;
  --surface:  #1c1a17;
  --surface2: #242119;
  --border:   #332e27;
  --border2:  #4a4237;
  --text:     #e8e2d8;
  --muted:    #9a8e80;
  --hi:       rgba(200,75,47,0.1);
}

/* ── Reset ── */
*,*::before,*::after { margin:0; padding:0; box-sizing:border-box; }
html { scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--sans);
  min-height: 100vh;
  overflow-x: hidden;
  line-height: 1.6;
  transition: background .3s var(--ease), color .3s var(--ease);
}

/* Grain overlay */
body::after {
  content: '';
  position: fixed; inset: 0;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='300' height='300'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='300' height='300' filter='url(%23n)' opacity='0.025'/%3E%3C/svg%3E");
  pointer-events: none;
  z-index: 9999;
}

/* ── Header ── */
header {
  position: fixed; top: 0; left: 0; right: 0;
  height: var(--hdr-h);
  background: var(--bg);
  border-bottom: 1px solid var(--border);
  display: flex; align-items: center;
  padding: 0 28px 0 20px;
  gap: 16px;
  z-index: 200;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}

.logo-ring {
  width: 36px; height: 36px;
  border: 2px solid var(--accent);
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  flex-shrink: 0;
  cursor: pointer;
}
.logo-ring::after {
  content: '';
  width: 10px; height: 10px;
  background: var(--accent);
  border-radius: 50%;
  animation: pulse 2s ease-in-out infinite;
}
@keyframes pulse { 0%,100% { transform:scale(1); opacity:1; } 50% { transform:scale(1.4); opacity:.6; } }

header h1 {
  font-family: var(--serif);
  font-size: 20px; font-weight: 700;
  letter-spacing: -.01em;
  color: var(--text);
}
header h1 em { font-style: italic; color: var(--accent); }

.hdr-meta {
  margin-left: auto;
  font-family: var(--mono);
  font-size: 11px; color: var(--muted);
  text-align: right; line-height: 1.6;
}

.hdr-actions {
  display: flex; gap: 8px; align-items: center;
  margin-left: 16px;
}

.theme-toggle {
  width: 34px; height: 34px;
  border: 1px solid var(--border);
  border-radius: 50%;
  background: var(--surface);
  color: var(--muted);
  cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  font-size: 16px;
  transition: all .2s var(--ease);
}
.theme-toggle:hover { border-color: var(--accent); color: var(--accent); transform: rotate(20deg); }
.theme-toggle:active { transform: rotate(20deg) scale(.92); }

.search-toggle {
  width: 34px; height: 34px;
  border: 1px solid var(--border);
  border-radius: 50%;
  background: var(--surface);
  color: var(--muted);
  cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  font-size: 15px;
  transition: all .2s var(--ease);
}
.search-toggle:hover { border-color: var(--accent); color: var(--accent); }
.search-toggle:active { transform: scale(.92); }

.topic-counter {
  background: var(--accent);
  color: #fff;
  font-family: var(--mono);
  font-size: 10px; font-weight: 500;
  padding: 3px 9px;
  border-radius: 20px;
  letter-spacing: .05em;
}

/* ── Search overlay ── */
.search-overlay {
  position: fixed; inset: 0;
  background: rgba(0,0,0,.5);
  z-index: 300;
  display: none;
  align-items: flex-start;
  justify-content: center;
  padding-top: 120px;
  backdrop-filter: blur(4px);
}
.search-overlay.active { display: flex; }
.search-box {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  width: 560px;
  max-width: 90vw;
  box-shadow: var(--shadow-lg);
  overflow: hidden;
}
.search-input {
  width: 100%;
  padding: 18px 20px;
  border: none;
  background: transparent;
  font-family: var(--mono);
  font-size: 15px;
  color: var(--text);
  outline: none;
}
.search-input::placeholder { color: var(--muted); }
.search-results {
  max-height: 340px;
  overflow-y: auto;
  border-top: 1px solid var(--border);
}
.search-result {
  padding: 12px 20px;
  cursor: pointer;
  transition: background .12s;
  border-bottom: 1px solid var(--border);
}
.search-result:hover { background: var(--hi); }
.search-result:last-child { border-bottom: none; }
.sr-title { font-weight: 600; font-size: 14px; color: var(--text); }
.sr-cat { font-family: var(--mono); font-size: 10px; color: var(--muted); letter-spacing: .1em; text-transform: uppercase; }
.search-hint {
  display: flex; align-items: center; gap: 4px;
  padding: 10px 20px;
  font-family: var(--mono); font-size: 10px; color: var(--border2);
  border-top: 1px solid var(--border);
}

/* ── Layout ── */
.layout {
  display: grid;
  grid-template-columns: var(--nav-w) 1fr;
  margin-top: var(--hdr-h);
  min-height: calc(100vh - var(--hdr-h));
}

/* ── Sidebar nav ── */
nav {
  border-right: 1px solid var(--border);
  padding: 16px 0 32px;
  position: sticky;
  top: var(--hdr-h);
  height: calc(100vh - var(--hdr-h));
  overflow-y: auto;
  background: var(--bg);
}
nav::-webkit-scrollbar { width: 4px; }
nav::-webkit-scrollbar-track { background: transparent; }
nav::-webkit-scrollbar-thumb { background: var(--border2); border-radius: 2px; }

.nav-section { margin-bottom: 4px; }
.nav-section-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 10px 16px 6px;
  cursor: pointer;
  user-select: none;
}
.nav-section-title {
  font-family: var(--mono);
  font-size: 9px; letter-spacing: .18em;
  text-transform: uppercase;
  color: var(--muted);
  font-weight: 500;
}
.nav-section-arrow {
  font-size: 10px; color: var(--muted);
  transition: transform .2s var(--ease);
}
.nav-section.open .nav-section-arrow { transform: rotate(180deg); }

.nav-items {
  overflow: hidden;
  max-height: 0;
  transition: max-height .3s var(--ease);
}
.nav-section.open .nav-items { max-height: 800px; }

.ni {
  display: flex; align-items: center; gap: 9px;
  padding: 7px 16px 7px 20px;
  cursor: pointer;
  transition: all .15s var(--ease);
  font-size: 13px;
  color: var(--muted);
  font-family: var(--sans);
  font-weight: 400;
  border-left: 2px solid transparent;
  line-height: 1.3;
  position: relative;
}
.ni:hover { color: var(--text); background: var(--surface2); padding-left: 24px; }
.ni.active {
  color: var(--accent);
  background: var(--hi);
  border-left-color: var(--accent);
  font-weight: 600;
  padding-left: 24px;
}
.ni:active { transform: scale(.98); }
.ni-num {
  font-family: var(--mono);
  font-size: 9px; color: var(--border2);
  flex-shrink: 0; width: 20px;
  transition: color .15s;
}
.ni:hover .ni-num { color: var(--text); }
.ni.active .ni-num { color: var(--accent); }

/* ── Progress bar ── */
.nav-progress {
  margin: 12px 16px 8px;
  height: 3px;
  background: var(--border);
  border-radius: 2px;
  overflow: hidden;
}
.nav-progress-bar {
  height: 100%;
  background: var(--accent);
  border-radius: 2px;
  transition: width .3s var(--ease);
  width: 0%;
}
.nav-progress-text {
  font-family: var(--mono);
  font-size: 9px;
  color: var(--muted);
  padding: 0 16px 8px;
  letter-spacing: .08em;
}

/* ── Main content ── */
main {
  padding: 40px 56px 80px;
  max-width: 900px;
}

/* ── Home / overview page ── */
.home { display: none; }
.home.active { display: block; animation: fi .3s var(--ease); }

.home-hero {
  border-bottom: 1px solid var(--border);
  padding-bottom: 32px;
  margin-bottom: 36px;
}
.home-hero h2 {
  font-family: var(--serif);
  font-size: clamp(32px,5vw,56px);
  font-weight: 400;
  line-height: 1.1;
  letter-spacing: -.02em;
  margin-bottom: 12px;
}
.home-hero h2 em { font-style: italic; color: var(--accent); }
.home-hero p {
  font-family: var(--mono);
  font-size: 13px; color: var(--muted);
  max-width: 560px; line-height: 1.7;
}

.cat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px,1fr));
  gap: 14px;
  margin-bottom: 36px;
}
.cat-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px 22px;
  cursor: pointer;
  transition: all .2s var(--ease);
  position: relative;
  overflow: hidden;
}
.cat-card::after {
  content: '';
  position: absolute; bottom: 0; left: 0; right: 0;
  height: 2px;
  background: var(--accent);
  transform: scaleX(0);
  transition: transform .25s var(--ease);
}
.cat-card:hover {
  border-color: var(--accent);
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
}
.cat-card:hover::after { transform: scaleX(1); }
.cat-card:active { transform: translateY(-1px); }
.cat-card-icon {
  font-size: 22px; margin-bottom: 10px;
  width: 42px; height: 42px;
  display: flex; align-items: center; justify-content: center;
  background: var(--hi);
  border-radius: 10px;
  transition: transform .2s var(--ease);
}
.cat-card:hover .cat-card-icon { transform: scale(1.08); }
.cat-card-name { font-size: 15px; font-weight: 700; margin-bottom: 4px; color: var(--text); }
.cat-card-count { font-family: var(--mono); font-size: 11px; color: var(--muted); line-height: 1.5; }

/* ── Topic page ── */
.topic { display: none; }
.topic.active { display: block; animation: fi .25s var(--ease); }
@keyframes fi { from { opacity:0; transform:translateY(10px); } to { opacity:1; transform:translateY(0); } }
@keyframes fadeUp { from { opacity:0; transform:translateY(16px); } to { opacity:1; transform:translateY(0); } }

.topic-header {
  display: flex; align-items: flex-start; gap: 16px;
  margin-bottom: 6px;
  padding-bottom: 20px;
  border-bottom: 1px solid var(--border);
}
.topic-meta { flex: 1; }
.topic-num {
  font-family: var(--mono);
  font-size: 11px; color: var(--muted);
  margin-bottom: 4px;
  letter-spacing: .08em;
}

h2 {
  font-family: var(--serif);
  font-size: clamp(26px,3.5vw,40px);
  font-weight: 700;
  letter-spacing: -.02em;
  line-height: 1.1;
}
h2 em { font-style: italic; color: var(--accent); }

.topic-badge {
  font-family: var(--mono);
  font-size: 10px;
  padding: 4px 10px;
  border-radius: 20px;
  border: 1px solid var(--border);
  color: var(--muted);
  background: var(--surface2);
  flex-shrink: 0;
  margin-top: 4px;
}

.sub {
  font-family: var(--mono);
  font-size: 12px; color: var(--muted);
  margin: 14px 0 22px;
  line-height: 1.7;
  padding: 10px 0;
}

/* ── Prose ── */
.prose {
  font-size: 16px;
  line-height: 1.85;
  color: var(--muted);
  margin-bottom: 18px;
  font-weight: 400;
}
.prose strong { color: var(--text); font-weight: 700; }

/* ── Formula boxes ── */
.fb {
  background: var(--surface);
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent);
  border-radius: 8px;
  padding: 16px 20px;
  margin: 16px 0;
  position: relative;
  overflow: hidden;
}
.fb::after {
  content: 'FORMULA';
  position: absolute; top: 8px; right: 12px;
  font-family: var(--mono);
  font-size: 8px; letter-spacing: .2em;
  color: var(--accent);
  opacity: .35;
}
.fb.c2 { border-left-color: var(--accent2); }
.fb.c2::after { color: var(--accent2); }
.fb.c3 { border-left-color: var(--accent3); }
.fb.c3::after { color: var(--accent3); }
.fb.c4 { border-left-color: var(--accent4); }
.fb.c4::after { color: var(--accent4); }

.fm {
  font-family: var(--mono);
  font-size: 15px;
  color: var(--accent);
  margin-bottom: 8px;
  letter-spacing: .02em;
  line-height: 1.5;
}
.fb.c2 .fm { color: var(--accent2); }
.fb.c3 .fm { color: var(--accent3); }
.fb.c4 .fm { color: var(--accent4); }

.fd {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--muted);
  line-height: 1.8;
}
.fd span { color: var(--text); }

/* ── Visualization area ── */
.va {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  margin: 20px 0;
  position: relative;
  overflow: hidden;
}
.va::before {
  content: '';
  position: absolute; top: 0; left: 0; right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--accent), var(--accent2), var(--accent3));
  opacity: .5;
  border-radius: var(--radius) var(--radius) 0 0;
}
.vl {
  font-family: var(--mono);
  font-size: 10px; color: var(--muted);
  letter-spacing: .12em;
  margin-bottom: 12px;
  text-transform: uppercase;
  display: flex; align-items: center; gap: 6px;
}
.vl::before {
  content: '▸';
  color: var(--accent);
  font-size: 8px;
}
canvas {
  display: block;
  width: 100%;
  border-radius: 6px;
  background: var(--bg);
}

.ctrl {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 14px;
  align-items: flex-end;
}
.cg { display: flex; flex-direction: column; gap: 4px; }
.cl { font-family: var(--mono); font-size: 10px; color: var(--muted); }

input[type=range] {
  -webkit-appearance: none;
  appearance: none;
  width: 120px; height: 3px;
  background: var(--border);
  border-radius: 2px;
  outline: none;
  cursor: pointer;
}
input[type=range]::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 14px; height: 14px;
  background: var(--accent);
  border-radius: 50%;
  cursor: pointer;
  box-shadow: 0 0 0 3px rgba(200,75,47,.15);
  transition: box-shadow .15s var(--ease);
}
input[type=range]::-webkit-slider-thumb:hover {
  box-shadow: 0 0 0 5px rgba(200,75,47,.2);
}
input[type=range]::-moz-range-thumb {
  width: 14px; height: 14px;
  background: var(--accent);
  border: none;
  border-radius: 50%;
  cursor: pointer;
  box-shadow: 0 0 0 3px rgba(200,75,47,.15);
}
input[type=range]::-moz-range-track {
  height: 3px;
  background: var(--border);
  border-radius: 2px;
  border: none;
}
input[type=range]:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 4px;
  border-radius: 2px;
}
.vd {
  font-family: var(--mono);
  font-size: 13px;
  color: var(--accent);
}

/* ── Buttons ── */
.btn {
  font-family: var(--mono);
  font-size: 10px; letter-spacing: .06em;
  padding: 7px 14px;
  background: transparent;
  border: 1px solid var(--accent);
  color: var(--accent);
  border-radius: 5px;
  cursor: pointer;
  transition: all .15s var(--ease);
  position: relative;
  overflow: hidden;
}
.btn:hover { background: var(--accent); color: #fff; box-shadow: 0 2px 8px rgba(200,75,47,.25); }
.btn:active { transform: scale(.96); }
.btn.b2 { border-color: var(--accent2); color: var(--accent2); }
.btn.b2:hover { background: var(--accent2); color: #fff; box-shadow: 0 2px 8px rgba(42,125,95,.25); }
.btn.b3 { border-color: var(--accent3); color: var(--accent3); }
.btn.b3:hover { background: var(--accent3); color: #fff; box-shadow: 0 2px 8px rgba(41,85,160,.25); }
.btn.b4 { border-color: var(--accent4); color: var(--accent4); }
.btn.b4:hover { background: var(--accent4); color: #fff; box-shadow: 0 2px 8px rgba(139,79,168,.25); }
.btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

/* ── Code blocks ── */
.code-block {
  background: #1c1917;
  border-radius: 8px;
  padding: 18px 20px;
  margin: 16px 0;
  overflow-x: auto;
  position: relative;
}
.code-block::before {
  content: 'Python';
  position: absolute; top: 8px; right: 12px;
  font-family: var(--mono);
  font-size: 9px; letter-spacing: .12em;
  color: #6b6256;
  text-transform: uppercase;
}
.code-block pre {
  font-family: var(--mono);
  font-size: 12px; line-height: 1.75;
  color: #d4c8b8;
}
.kw  { color: #e0855a; }
.cl2 { color: #70b8a8; }
.fn  { color: #a4b8e0; }
.st  { color: #b8d496; }
.cm  { color: #6b6256; font-style: italic; }

/* ── Steps / walkthrough ── */
.steps { display: grid; gap: 8px; margin: 16px 0; }
.step {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 12px 15px;
  display: grid;
  grid-template-columns: 24px 1fr;
  gap: 12px;
  align-items: start;
  transition: all .12s var(--ease);
}
.step:hover { border-color: var(--accent); background: var(--hi); }
.sn {
  font-family: var(--mono);
  font-size: 10px; color: var(--accent);
  background: var(--hi);
  width: 22px; height: 22px;
  display: flex; align-items: center; justify-content: center;
  border-radius: 4px;
  border: 1px solid rgba(200,75,47,.2);
  flex-shrink: 0;
}
.step h4 { font-size: 14px; font-weight: 700; margin-bottom: 2px; }
.step p { font-family: var(--mono); font-size: 11px; color: var(--muted); line-height: 1.5; }

/* ── Tables ── */
.mt {
  width: 100%;
  border-collapse: collapse;
  font-family: var(--mono);
  font-size: 11px;
  margin: 16px 0;
}
.mt th {
  text-align: left;
  padding: 8px 10px;
  border-bottom: 1px solid var(--accent);
  color: var(--accent);
  font-size: 9px; letter-spacing: .15em;
  text-transform: uppercase;
}
.mt td {
  padding: 8px 10px;
  border-bottom: 1px solid var(--border);
  color: var(--muted);
  line-height: 1.5;
}
.mt td:first-child { color: var(--text); }
.mt tr:hover td { background: var(--surface2); }

/* ── Tags ── */
.tag {
  display: inline-block;
  font-family: var(--mono);
  font-size: 9px;
  padding: 2px 7px;
  border-radius: 3px;
}
.t1 { background: rgba(200,75,47,.1); color: var(--accent); }
.t2 { background: rgba(42,125,95,.1); color: var(--accent2); }
.t3 { background: rgba(41,85,160,.1); color: var(--accent3); }
.t4 { background: rgba(139,79,168,.1); color: var(--accent4); }

/* ── Callouts ── */
.callout {
  background: rgba(42,125,95,.05);
  border: 1px solid rgba(42,125,95,.2);
  border-radius: 8px;
  padding: 14px 18px;
  margin: 16px 0;
  font-size: 13px;
  color: var(--accent2);
  line-height: 1.7;
  font-family: var(--mono);
}
.callout strong { color: var(--accent2); }
.callout::before {
  content: '💡';
  margin-right: 6px;
}
.callout.warn {
  background: rgba(200,75,47,.05);
  border-color: rgba(200,75,47,.2);
  color: var(--accent);
}
.callout.warn strong { color: var(--accent); }
.callout.warn::before { content: '⚠️'; }
.callout.info {
  background: rgba(41,85,160,.05);
  border-color: rgba(41,85,160,.2);
  color: var(--accent3);
}
.callout.info strong { color: var(--accent3); }
.callout.info::before { content: 'ℹ️'; }

/* ── Topic navigation ── */
.topic-nav {
  display: flex; gap: 12px;
  margin-top: 40px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}
.tnav-btn {
  flex: 1;
  padding: 14px 18px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
  transition: all .12s var(--ease);
  text-align: left;
}
.tnav-btn:hover { border-color: var(--accent); background: var(--hi); transform: translateY(-2px); box-shadow: var(--shadow-sm); }
.tnav-btn:active { transform: translateY(0); }
.tnav-dir {
  font-family: var(--mono);
  font-size: 10px; color: var(--muted);
  margin-bottom: 4px;
  transition: color .15s;
}
.tnav-btn:hover .tnav-dir { color: var(--accent); }
.tnav-name { font-size: 14px; font-weight: 700; color: var(--text); }
.tnav-btn.next { text-align: right; }

/* ── Keyboard shortcut hints ── */
.kbd {
  font-family: var(--mono);
  font-size: 10px;
  padding: 2px 6px;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 3px;
  color: var(--muted);
}

/* ── Portal-specific: collection cards ── */
.portal-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 24px;
  margin: 40px 0;
}
.collection-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 32px;
  cursor: pointer;
  transition: all .25s var(--ease);
  text-decoration: none;
  color: inherit;
  display: block;
  position: relative;
  overflow: hidden;
}
.collection-card::before {
  content: '';
  position: absolute; top: 0; left: 0; right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--accent), var(--accent2));
  opacity: 0;
  transition: opacity .25s var(--ease);
}
.collection-card:hover::before { opacity: 1; }
.collection-card:hover {
  border-color: var(--accent);
  transform: translateY(-6px);
  box-shadow: 0 12px 40px rgba(0,0,0,.1), 0 2px 8px rgba(0,0,0,.06);
}
.collection-card:active { transform: translateY(-2px); }
.cc-icon {
  font-size: 28px;
  margin-bottom: 16px;
  width: 52px; height: 52px;
  display: flex; align-items: center; justify-content: center;
  background: var(--hi);
  border-radius: 12px;
  border: 1px solid rgba(200,75,47,.12);
}
.cc-title {
  font-family: var(--serif);
  font-size: 24px; font-weight: 700;
  margin-bottom: 10px;
}
.cc-title em { font-style: italic; color: var(--accent); }
.cc-desc {
  font-family: var(--sans);
  font-size: 13px; color: var(--muted);
  line-height: 1.75;
  margin-bottom: 14px;
}
.cc-meta {
  font-family: var(--mono);
  font-size: 10px; color: var(--border2);
  letter-spacing: .08em;
  text-transform: uppercase;
}
.cc-tags { display: flex; gap: 6px; margin-top: 14px; flex-wrap: wrap; }

/* ── Responsive ── */
@media (max-width: 720px) {
  :root { --nav-w: 0px; }
  header { padding: 0 14px; }
  .hdr-meta { display: none; }
  .layout { grid-template-columns: 1fr; }
  nav {
    position: relative;
    height: auto; top: 0;
    border-right: none;
    border-bottom: 1px solid var(--border);
    display: flex;
    overflow-x: auto;
    padding: 8px;
    gap: 0;
    flex-wrap: nowrap;
  }
  .nav-section { flex-shrink: 0; }
  .nav-section-header { padding: 6px 10px; }
  .nav-section-title { display: none; }
  .nav-items { max-height: none !important; display: flex; flex-wrap: nowrap; }
  .ni {
    white-space: nowrap;
    border-left: none;
    border-bottom: 2px solid transparent;
    padding: 6px 10px;
  }
  .ni.active { border-bottom-color: var(--accent); background: var(--hi); }
  main { padding: 20px 16px 60px; }
  .portal-grid { grid-template-columns: 1fr; }
  .search-box { width: 95vw; }
}

/* ── Focus-visible for accessibility ── */
a:focus-visible, button:focus-visible, .ni:focus-visible, .cat-card:focus-visible, .collection-card:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* ── Selection color ── */
::selection {
  background: rgba(200,75,47,.15);
  color: var(--text);
}

/* ── Smooth nav scroll shadow ── */
nav {
  mask-image: linear-gradient(to bottom, transparent, black 8px, black calc(100% - 8px), transparent);
  -webkit-mask-image: linear-gradient(to bottom, transparent, black 8px, black calc(100% - 8px), transparent);
}

/* ── Code block hover ── */
.code-block {
  transition: box-shadow .2s var(--ease);
}
.code-block:hover {
  box-shadow: 0 4px 20px rgba(0,0,0,.3);
}

/* ── Formula box hover ── */
.fb {
  transition: border-color .2s var(--ease), box-shadow .2s var(--ease);
}
.fb:hover {
  box-shadow: var(--shadow-sm);
}

/* ── Portal animations ── */
.portal-hero { animation: fadeUp .5s var(--ease) both; }
.portal-stats { animation: fadeUp .5s .1s var(--ease) both; }
.portal-content { animation: fadeUp .5s .2s var(--ease) both; }
.portal-footer { animation: fadeUp .4s .3s var(--ease) both; }

/* ── Tag hover ── */
.tag { transition: transform .12s var(--ease); }
.tag:hover { transform: scale(1.06); }

/* ═══════════════════════════════════════════════════════════════
   PRINT STYLES
   ═══════════════════════════════════════════════════════════════ */
@media print {
  * { animation: none !important; transition: none !important; }
  body { padding: 0; background: white; color: #1a1a1a; font-size: 11pt; }
  header, nav, .search-overlay, .theme-toggle, .search-toggle,
  .topic-nav, .nav-progress, .nav-progress-text, .portal-header,
  .hdr-actions, .ctrl, .back-link, .portal-stats, .portal-footer { display: none !important; }
  .layout { display: block; }
  main { max-width: 100%; padding: 0; }
  .topic { display: block !important; page-break-inside: avoid; margin-bottom: 24pt; }
  .topic-header { margin-bottom: 8pt; }
  .topic-num { color: #666; }
  h2 em { color: #333 !important; }
  .home { display: none !important; }
  .fb { border-color: #999; break-inside: avoid; }
  .va { break-inside: avoid; }
  .va canvas { max-width: 100%; height: auto; }
  .code-block { border: 1px solid #ccc; break-inside: avoid; box-shadow: none; }
  .callout { border: 1px solid #ccc; break-inside: avoid; }
  .mt { border-collapse: collapse; }
  .mt th, .mt td { border: 1px solid #ccc; padding: 4pt 8pt; }
  a { color: inherit; text-decoration: none; }
  .collection-card { border: 1px solid #ccc; break-inside: avoid; }
  .portal-grid, .cat-grid { gap: 12pt; }
}