/* =============================================================
   DBMS Illustrated — style.css  v2.0
   Editorial dark redesign. Mirrors System Design Illustrated.
   Playfair Display + Inter + JetBrains Mono. Purple glow system.
   No emojis in CSS comments. Pure design tokens.
   ============================================================= */
@import url('https://fonts.googleapis.com/css2?family=Playfair+Display:ital,wght@0,400;0,600;0,700;0,900;1,400;1,700&family=Inter:wght@300;400;500;600;700&family=JetBrains+Mono:wght@300;400;500;700&display=swap');

/* ── CSS variables (dark default) ───────────────────────────── */
:root {
  --bg:          #05030e;
  --surface:     #130f26;
  --surface-2:   #1b1638;
  --surface-3:   #22194a;
  --primary:        #7C3AED;
  --primary-soft:   #A78BFA;
  --primary-faint:  rgba(124,58,237,0.12);
  --secondary:  #F59E0B;
  --accent:     #10B981;
  --error:      #EF4444;
  --text:       #EDE9FE;
  --text-soft:  #9490B4;
  --text-muted: #5C577A;
  --border:         rgba(124,58,237,0.32);
  --border-hi:      rgba(167,139,250,0.55);
  --shadow-sm:  0 2px 10px rgba(0,0,0,0.55);
  --shadow-md:  0 8px 28px rgba(0,0,0,0.65);
  --shadow-lg:  0 20px 56px rgba(124,58,237,0.28);
  --glow:       0 0 20px rgba(124,58,237,0.4);
  --font-display: 'Playfair Display', Georgia, serif;
  --font-head:    'Playfair Display', Georgia, serif;
  --font-body:    'Inter', system-ui, sans-serif;
  --font-mono:    'JetBrains Mono', 'Fira Code', monospace;
  --radius:    10px;
  --radius-sm: 6px;
  --radius-lg: 16px;
  --transition: 0.3s cubic-bezier(0.22,1,0.36,1);
  --topic-color: #7C3AED;
}

[data-theme="light"] {
  --bg:        #f5f3ff;
  --surface:   #ffffff;
  --surface-2: #f0ecff;
  --surface-3: #e8e3fa;
  --border:    rgba(124,58,237,0.18);
  --border-hi: rgba(124,58,237,0.4);
  --text:      #1a1535;
  --text-soft: #4a4668;
  --text-muted:#8884a0;
  --shadow-sm: 0 2px 8px rgba(33,29,53,0.07);
  --shadow-md: 0 8px 24px rgba(33,29,53,0.11);
  --shadow-lg: 0 20px 48px rgba(124,58,237,0.16);
  --primary-faint: rgba(124,58,237,0.08);
  --glow:      0 0 16px rgba(124,58,237,0.2);
}

/* ── Reset ──────────────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font-body);
  background: var(--bg);
  color: var(--text);
  line-height: 1.72;
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
  transition: background 0.4s ease, color 0.4s ease;
}
h1,h2,h3,h4 { font-family: var(--font-head); line-height: 1.2; }
a { color: var(--primary-soft); text-decoration: none; }
a:hover { color: var(--primary-soft); }
img,svg { max-width: 100%; }
table { border-collapse: collapse; width: 100%; }
code {
  font-family: var(--font-mono); font-size: 0.88em;
  background: var(--surface-2); border: 1px solid var(--border);
  padding: 0.1em 0.4em; border-radius: 4px; color: var(--primary-soft);
}
::selection { background: var(--primary); color: #fff; }

/* ── Reading progress bar ───────────────────────────────────── */
.reading-progress {
  position: fixed; top: 0; left: 0;
  height: 2px; width: 0%;
  background: linear-gradient(90deg, var(--primary), var(--secondary));
  z-index: 1001;
  border-radius: 0 2px 2px 0;
  box-shadow: 0 0 14px var(--primary), 0 0 28px rgba(124,58,237,0.4);
  transition: width 80ms linear;
}
/* compat: older pages use #scroll-progress inside .topic-progress */
.topic-progress { display: none; }
#scroll-progress { display: none; }

/* ── Navbar ─────────────────────────────────────────────────── */
.navbar {
  position: fixed; top: 0; left: 0; right: 0; z-index: 1000;
  background: color-mix(in srgb, var(--surface) 72%, transparent);
  backdrop-filter: blur(20px) saturate(180%);
  -webkit-backdrop-filter: blur(20px) saturate(180%);
  border-bottom: 1px solid var(--border);
  transition: background var(--transition);
}
.navbar-inner {
  max-width: 1180px; margin: 0 auto;
  padding: 0.8rem 1.5rem;
  display: flex; align-items: center; justify-content: space-between; gap: 1rem;
}
.navbar-brand {
  font-family: var(--font-head); font-weight: 700; font-size: 1.08rem;
  color: var(--text); display: flex; align-items: center; gap: 0.45rem;
  white-space: nowrap;
}
.brand-icon { filter: drop-shadow(0 0 6px rgba(124,58,237,0.6)); }
.navbar-links { display: flex; align-items: center; gap: 1.4rem; }
.navbar-links a {
  font-family: var(--font-mono); font-size: 0.82rem; letter-spacing: 0.05em;
  color: var(--text-soft); font-weight: 500;
  transition: color var(--transition);
  position: relative;
}
.navbar-links a::after {
  content: ''; position: absolute; left: 0; bottom: -3px;
  width: 0; height: 1px; background: var(--primary-soft);
  transition: width var(--transition);
}
.navbar-links a:hover { color: var(--primary-soft); }
.navbar-links a:hover::after { width: 100%; }
.btn-icon {
  background: var(--surface-2); border: 1px solid var(--border);
  border-radius: 50%; width: 36px; height: 36px; cursor: pointer;
  display: grid; place-items: center; font-size: 1rem;
  transition: transform var(--transition), box-shadow var(--transition);
}
.btn-icon:hover { transform: rotate(22deg) scale(1.1); box-shadow: 0 0 14px var(--primary); }

/* ── Scroll reveal ──────────────────────────────────────────── */
.reveal {
  opacity: 0;
  transform: translateY(28px);
  transition: opacity 0.65s ease, transform 0.65s cubic-bezier(0.22,1,0.36,1);
}
.reveal.visible { opacity: 1; transform: none; }

/* ── Container ──────────────────────────────────────────────── */
.container {
  max-width: 820px; margin: 0 auto; padding: 0 1.4rem;
  padding-top: 5rem;
}

/* ── Breadcrumb ─────────────────────────────────────────────── */
.breadcrumb {
  font-family: var(--font-mono); font-size: 0.72rem; letter-spacing: 0.08em;
  color: var(--text-muted); margin: 1.2rem 0 0.6rem;
}
.breadcrumb a { color: var(--text-muted); }
.breadcrumb a:hover { color: var(--primary-soft); }
.breadcrumb-sep { margin: 0 0.4rem; opacity: 0.5; }

/* ── Topic header ───────────────────────────────────────────── */
.topic-header {
  padding: 2rem 0 1.6rem;
  border-bottom: 1px solid var(--border);
  margin-bottom: 2.4rem;
}
.topic-badge {
  display: inline-block;
  font-family: var(--font-mono); font-size: 0.68rem; font-weight: 700;
  letter-spacing: 0.22em; text-transform: uppercase;
  color: var(--topic-color);
  background: color-mix(in srgb, var(--topic-color) 12%, transparent);
  border: 1px solid color-mix(in srgb, var(--topic-color) 35%, transparent);
  padding: 0.25rem 0.8rem; border-radius: 999px; margin-bottom: 0.9rem;
}
.topic-header h1 {
  font-size: clamp(2rem, 5vw, 3.2rem);
  font-weight: 700; line-height: 1.1;
  color: var(--text); margin-bottom: 0.7rem;
}
.topic-header h1 .accent { color: var(--topic-color); font-style: italic; }
.subtitle {
  font-size: 1.05rem; color: var(--text-soft); line-height: 1.7;
  max-width: 66ch; margin-bottom: 1rem;
}
.topic-meta { display: flex; gap: 0.5rem; flex-wrap: wrap; margin: 0.8rem 0; }
.tag {
  font-family: var(--font-mono); font-size: 0.73rem; letter-spacing: 0.06em;
  color: var(--text-soft); background: var(--surface-2);
  border: 1px solid var(--border); padding: 0.25rem 0.7rem;
  border-radius: 999px;
}

/* ── Company badges ─────────────────────────────────────────── */
.company-badges { display: flex; flex-wrap: wrap; gap: 0.5rem; margin: 0.8rem 0; }
.badge {
  font-family: var(--font-mono); font-size: 0.72rem; font-weight: 600;
  letter-spacing: 0.05em; color: var(--text-soft);
  background: var(--surface-2); border: 1px solid var(--border);
  padding: 0.28rem 0.72rem; border-radius: 999px;
  transition: border-color var(--transition), color var(--transition);
}
.badge:hover { border-color: var(--primary-soft); color: var(--primary-soft); }

/* ── At-a-glance box ────────────────────────────────────────── */
.at-a-glance {
  background: var(--primary-faint);
  border: 1px solid var(--border-hi);
  border-radius: var(--radius);
  padding: 1.4rem 1.6rem;
  margin: 0 0 2.2rem;
}
.at-a-glance h3 {
  font-family: var(--font-mono); font-size: 0.75rem; letter-spacing: 0.18em;
  text-transform: uppercase; color: var(--primary-soft); margin-bottom: 0.85rem;
}
.at-a-glance ul { list-style: none; display: flex; flex-direction: column; gap: 0.45rem; }
.at-a-glance li {
  font-size: 0.93rem; color: var(--text-soft); line-height: 1.6;
  padding-left: 1.2em; position: relative;
}
.at-a-glance li::before { content: '->'; position: absolute; left: 0; color: var(--primary-soft); font-weight: 700; font-family: var(--font-mono); font-size: 0.75rem; top: 0.15em; }
.at-a-glance li strong { color: var(--text); }

/* ── Section block ──────────────────────────────────────────── */
.section-block { margin: 2.8rem 0; }
.section-block h2 {
  font-size: 1.65rem; font-weight: 700; color: var(--text);
  margin-bottom: 0.9rem; padding-bottom: 0.55rem;
  border-bottom: 1px solid var(--border);
}
.section-block h3 {
  font-size: 1.1rem; font-weight: 600; color: var(--text); margin: 1.4rem 0 0.5rem;
}
.section-block p {
  color: var(--text-soft); font-size: 0.97rem; line-height: 1.78; margin-bottom: 0.85rem;
}
.section-block p strong { color: var(--text); }

/* ── Section label (small caps) ─────────────────────────────── */
.section-label {
  font-family: var(--font-mono); font-size: 0.68rem; font-weight: 700;
  letter-spacing: 0.22em; text-transform: uppercase;
  color: var(--topic-color); margin: 2.8rem 0 0.6rem;
}
.section-title {
  font-size: 1.65rem; font-weight: 700; margin-bottom: 1rem;
  padding-bottom: 0.55rem; border-bottom: 1px solid var(--border);
}
.section-desc { color: var(--text-soft); font-size: 0.96rem; margin-bottom: 1.4rem; line-height: 1.7; }

/* ── Mini cards ─────────────────────────────────────────────── */
.mini-cards {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(210px,1fr));
  gap: 1rem; margin: 1.2rem 0 2rem;
}
.mini-card {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 1.2rem;
  transition: border-color var(--transition), box-shadow var(--transition), transform 0.2s ease;
}
.mini-card:hover {
  border-color: color-mix(in srgb, var(--topic-color) 60%, transparent);
  box-shadow: 0 4px 20px color-mix(in srgb, var(--topic-color) 18%, transparent);
  transform: translateY(-3px);
}
.mini-card-icon { font-size: 1.5rem; margin-bottom: 0.6rem; display: block; line-height: 1; }
.mini-card h4 { font-size: 0.96rem; font-weight: 600; margin-bottom: 0.4rem; }
.mini-card p { font-size: 0.86rem; color: var(--text-soft); line-height: 1.65; margin: 0; }

/* ── Steps ──────────────────────────────────────────────────── */
.steps { display: flex; flex-direction: column; gap: 0.9rem; margin: 1.2rem 0 2rem; }
.step-item {
  display: flex; align-items: flex-start; gap: 1rem;
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius-sm); padding: 1.1rem 1.2rem;
  transition: border-color var(--transition), box-shadow var(--transition);
}
.step-item:hover {
  border-color: color-mix(in srgb, var(--topic-color) 50%, transparent);
  box-shadow: 0 2px 14px color-mix(in srgb, var(--topic-color) 12%, transparent);
}
.step-num {
  flex: none; width: 34px; height: 34px; border-radius: 50%;
  background: color-mix(in srgb, var(--topic-color) 18%, transparent);
  border: 1.5px solid color-mix(in srgb, var(--topic-color) 45%, transparent);
  color: var(--topic-color);
  font-family: var(--font-mono); font-size: 0.82rem; font-weight: 700;
  display: flex; align-items: center; justify-content: center;
  margin-top: 0.1rem;
}
.step-item > div:not(.step-num) { flex: 1; min-width: 0; }
.step-item h4 { font-size: 0.97rem; font-weight: 600; margin-bottom: 0.3rem; }
.step-item p { font-size: 0.88rem; color: var(--text-soft); line-height: 1.65; margin: 0; }

/* ── Diagram box ────────────────────────────────────────────── */
.diagram-box {
  background: color-mix(in srgb, var(--surface) 90%, transparent);
  border: 1px solid var(--border); border-radius: var(--radius);
  padding: 1.4rem; margin: 1.4rem 0; overflow-x: auto;
  transition: border-color 0.25s, box-shadow 0.25s;
}
.diagram-box:hover {
  border-color: rgba(124,58,237,0.5);
  box-shadow: 0 8px 32px rgba(124,58,237,0.14), inset 0 1px 0 rgba(255,255,255,0.04);
}
.diagram-box svg { display: block; max-width: 100%; margin: 0 auto; }
.diagram-caption {
  font-family: var(--font-mono); font-size: 0.75rem; letter-spacing: 0.04em;
  color: var(--text-muted); text-align: center; margin-top: 0.85rem;
}

/* ── SVG diagram helpers ────────────────────────────────────── */
.svg-label { font-family: var(--font-sans); font-size: 13px; font-weight: 600; fill: var(--text); }
.svg-soft  { font-family: var(--font-sans); font-size: 11px; fill: var(--text-soft); }
.svg-mono  { font-family: var(--font-mono); font-size: 11px; fill: var(--text-soft); }
.svg-box   { fill: var(--surface-2); stroke: var(--border); stroke-width: 1.5; }
.svg-box-p { fill: rgba(124,58,237,0.12); stroke: #7C3AED; stroke-width: 1.8; }
.svg-box-c { fill: rgba(14,165,233,0.10); stroke: #0EA5E9; stroke-width: 1.8; }
.svg-box-g { fill: rgba(16,185,129,0.10); stroke: #10B981; stroke-width: 1.8; }
.svg-box-a { fill: rgba(245,158,11,0.10); stroke: #F59E0B; stroke-width: 1.8; }
.svg-box-r { fill: rgba(239,68,68,0.10);  stroke: #EF4444; stroke-width: 1.8; }
.svg-line  { stroke: var(--text-muted); stroke-width: 1.8; fill: none; }
.svg-line-p { stroke: #7C3AED; stroke-width: 1.8; fill: none; opacity: 0.55; }
.svg-dash  { stroke-dasharray: 7 5; animation: svgDashMove 1.4s linear infinite; }
/* Animated packet circles — driven by initDiagramPackets() */
.pkt { opacity: 0; }
/* Sequential entrance animations */
.seq { opacity: 0; animation: svgSeqIn 0.6s ease forwards; }
.seq-1 { animation-delay: 0.15s; } .seq-2 { animation-delay: 0.5s; }
.seq-3 { animation-delay: 0.85s; } .seq-4 { animation-delay: 1.2s; }
.seq-5 { animation-delay: 1.55s; }
@keyframes svgDashMove { to { stroke-dashoffset: -24; } }
@keyframes svgSeqIn { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: none; } }

/* ── Code block ─────────────────────────────────────────────── */
.code-block {
  background: #08051a; border: 1px solid var(--border);
  border-radius: var(--radius); margin: 1.4rem 0; overflow: hidden;
}
.cb-header {
  display: flex; align-items: center; gap: 0.6rem;
  padding: 0.5rem 1rem; background: var(--surface-2);
  border-bottom: 1px solid var(--border);
}
.cb-dots { display: flex; gap: 5px; }
.cb-dot { width: 11px; height: 11px; border-radius: 50%; }
.cb-dot:nth-child(1) { background: #FF5F57; }
.cb-dot:nth-child(2) { background: #FFBD2E; }
.cb-dot:nth-child(3) { background: #28C940; }
.cb-lang {
  font-family: var(--font-mono); font-size: 0.73rem; letter-spacing: 0.08em;
  color: var(--text-muted); text-transform: uppercase;
}
.code-block pre {
  padding: 1.2rem 1.4rem; font-family: var(--font-mono);
  font-size: 0.84rem; line-height: 1.72; overflow-x: auto; color: #b8b1d6;
}
.code-block .kw  { color: #c792ea; }
.code-block .fn  { color: #82aaff; }
.code-block .str { color: #c3e88d; }
.code-block .num { color: #f78c6c; }
.code-block .cmt { color: #546e7a; font-style: italic; }

/* ── Table ──────────────────────────────────────────────────── */
.table-wrap { overflow-x: auto; margin: 1.2rem 0; border: 1px solid var(--border); border-radius: var(--radius); }
.compare-table { width: 100%; border-collapse: collapse; font-size: 0.88rem; }
.compare-table thead tr { background: var(--surface-2); }
.compare-table th {
  padding: 0.65rem 0.9rem; text-align: left;
  font-family: var(--font-mono); font-size: 0.72rem; letter-spacing: 0.1em;
  text-transform: uppercase; color: var(--primary-soft); font-weight: 600;
  border-bottom: 1px solid var(--border);
}
.compare-table td {
  padding: 0.62rem 0.9rem; color: var(--text-soft);
  border-bottom: 1px solid rgba(124,58,237,0.1);
  vertical-align: top;
}
.compare-table tr:last-child td { border-bottom: none; }
.compare-table tr:hover td { background: var(--primary-faint); }

/* ── Callout ─────────────────────────────────────────────────── */
.callout {
  display: flex; align-items: flex-start; gap: 0.85rem;
  border: 1px solid var(--border); border-radius: var(--radius-sm);
  padding: 1rem 1.1rem; margin: 1.2rem 0; background: var(--surface);
}
.callout-icon { font-size: 1.1rem; flex: none; margin-top: 0.1rem; }
.callout p { font-size: 0.9rem; color: var(--text-soft); margin: 0; line-height: 1.65; }
.callout p strong { color: var(--text); }
.callout.warn { border-color: rgba(245,158,11,0.4); background: rgba(245,158,11,0.05); }
.callout.tip  { border-color: rgba(16,185,129,0.4);  background: rgba(16,185,129,0.05); }
.callout.info { border-color: var(--border-hi);      background: var(--primary-faint); }

/* ── Interactive Demo shell ─────────────────────────────────── */
.demo-section {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); overflow: hidden; margin: 1.8rem 0;
  box-shadow: 0 4px 28px rgba(0,0,0,0.45), inset 0 1px 0 rgba(255,255,255,0.04);
}
.demo-header {
  display: flex; align-items: center; justify-content: space-between; gap: 0.8rem;
  padding: 0.75rem 1.2rem; background: var(--surface-2);
  border-bottom: 1px solid var(--border); flex-wrap: wrap;
}
.demo-header h3 {
  font-family: var(--font-mono); font-size: 0.85rem; font-weight: 500;
  letter-spacing: 0.05em; color: var(--text-soft); margin: 0;
}
.demo-controls { display: flex; gap: 0.5rem; flex-wrap: wrap; }
.demo-btn {
  font-family: var(--font-mono); font-size: 0.78rem; letter-spacing: 0.05em;
  padding: 0.4rem 0.85rem; border-radius: var(--radius-sm);
  border: 1px solid var(--border); background: var(--surface-3);
  color: var(--text-soft); cursor: pointer;
  transition: border-color var(--transition), color var(--transition), box-shadow var(--transition);
}
.demo-btn:hover { border-color: var(--primary-soft); color: var(--primary-soft); box-shadow: 0 0 10px rgba(124,58,237,0.2); }
.demo-btn.active { border-color: var(--primary-soft); color: var(--primary-soft); background: rgba(124,58,237,0.12); }
.demo-canvas-wrap {
  display: flex; align-items: center; justify-content: center;
  background: #05030e; min-height: 320px; padding: 1rem;
  position: relative; overflow: hidden;
}
.demo-canvas-wrap canvas { border-radius: 4px; display: block; }
.demo-hint {
  padding: 0.65rem 1.2rem;
  font-family: var(--font-mono); font-size: 0.73rem; letter-spacing: 0.04em;
  color: var(--text-muted); border-top: 1px solid var(--border);
  background: var(--surface-2);
}
.demo-input {
  font-family: var(--font-mono); font-size: 0.83rem;
  background: var(--surface-3); border: 1px solid var(--border);
  color: var(--text); border-radius: var(--radius-sm);
  padding: 0.38rem 0.7rem; outline: none; width: 220px;
  transition: border-color var(--transition);
}
.demo-input:focus { border-color: var(--primary-soft); box-shadow: 0 0 0 3px rgba(124,58,237,0.15); }

/* ── Quiz ───────────────────────────────────────────────────── */
.quiz-section { display: flex; flex-direction: column; gap: 1.8rem; margin: 1.4rem 0 2rem; }
.quiz-question {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 1.4rem 1.6rem;
  transition: border-color var(--transition);
}
.quiz-question:hover { border-color: var(--border-hi); }
.quiz-q-num {
  font-family: var(--font-mono); font-size: 0.68rem; letter-spacing: 0.14em;
  text-transform: uppercase; color: var(--primary-soft); margin-bottom: 0.55rem;
}
.quiz-q-text { font-size: 1rem; font-weight: 600; margin-bottom: 1rem; color: var(--text); line-height: 1.5; }
.quiz-options { display: flex; flex-direction: column; gap: 0.55rem; }
.quiz-option {
  display: flex; align-items: flex-start; gap: 0.75rem;
  padding: 0.75rem 1rem;
  background: var(--surface-2); border: 1px solid var(--border);
  border-radius: var(--radius-sm); cursor: pointer;
  font-size: 0.92rem; color: var(--text-soft); line-height: 1.55;
  transition: border-color var(--transition), background var(--transition);
  user-select: none;
}
.quiz-option:hover { border-color: var(--primary-soft); background: var(--primary-faint); }
.quiz-option.correct { border-color: #10B981; background: rgba(16,185,129,0.1); color: var(--text); }
.quiz-option.wrong   { border-color: #EF4444; background: rgba(239,68,68,0.1);  color: var(--text-muted); }
.quiz-option.disabled { pointer-events: none; }
.opt-letter {
  flex: none; width: 24px; height: 24px; border-radius: 50%;
  background: var(--surface-3); border: 1px solid var(--border);
  font-family: var(--font-mono); font-size: 0.75rem; font-weight: 700;
  display: flex; align-items: center; justify-content: center;
  color: var(--text-muted); margin-top: 0.05rem;
}
.quiz-feedback {
  display: none; margin-top: 1rem; padding: 0.9rem 1.1rem;
  border-radius: var(--radius-sm); font-size: 0.9rem; line-height: 1.65;
}
.quiz-feedback.show { display: block; animation: fadeUp 0.35s ease both; }
.quiz-feedback.correct-fb { background: rgba(16,185,129,0.08); border: 1px solid rgba(16,185,129,0.28); color: #34D399; }
.quiz-feedback.wrong-fb   { background: rgba(239,68,68,0.08);  border: 1px solid rgba(239,68,68,0.28);  color: #F87171; }

/* ── Q&A accordion ──────────────────────────────────────────── */
.qa-section { display: flex; flex-direction: column; gap: 0.6rem; margin: 1.2rem 0 2rem; }
.qa-item {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius-sm); overflow: hidden;
  transition: border-color var(--transition);
}
.qa-item:hover, .qa-item.open { border-color: var(--primary-soft); }
.qa-q {
  width: 100%; text-align: left; padding: 0.95rem 1.1rem;
  background: none; border: none; cursor: pointer;
  color: var(--text); font-size: 0.95rem; font-weight: 600;
  line-height: 1.5; font-family: var(--font-body);
  display: flex; align-items: center; justify-content: space-between; gap: 1rem;
}
.qa-chevron {
  flex: none; font-size: 1.1rem; color: var(--primary-soft);
  transition: transform 0.25s ease; display: inline-block;
}
.qa-item.open .qa-chevron { transform: rotate(180deg); }
.qa-a {
  max-height: 0; overflow: hidden;
  transition: max-height 0.4s cubic-bezier(0.4,0,0.2,1);
}
.qa-item.open .qa-a { max-height: 900px; }
.qa-a-inner {
  padding: 0.2rem 1.1rem 1rem;
  font-size: 0.9rem; color: var(--text-soft); line-height: 1.72;
}
.qa-a-inner strong { color: var(--text); }
.qa-a-inner code { font-size: 0.82em; }

/* ── Anti-patterns ──────────────────────────────────────────── */
.antipatterns { display: flex; flex-direction: column; gap: 0.9rem; margin: 1.2rem 0 2rem; }
.antipattern {
  background: var(--surface); border: 1px solid var(--border);
  border-left: 3px solid #EF4444; border-radius: var(--radius-sm);
  padding: 1rem 1.2rem;
  transition: border-color var(--transition), box-shadow var(--transition);
}
.antipattern:hover { border-left-color: #F87171; box-shadow: 0 4px 16px rgba(239,68,68,0.12); }
.antipattern h4 { font-size: 0.95rem; font-weight: 600; margin-bottom: 0.3rem; color: #F87171; }
.antipattern p  { font-size: 0.88rem; color: var(--text-soft); line-height: 1.65; margin: 0; }

/* ── Comparison grid (sharding, replication) ────────────────── */
.comparison-grid {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(260px,1fr));
  gap: 1rem; margin: 1.2rem 0 2rem;
}
.comparison-card {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 1.2rem 1.4rem;
  transition: border-color var(--transition), box-shadow var(--transition);
}
.comparison-card:hover { border-color: var(--primary); box-shadow: 0 4px 20px rgba(124,58,237,0.1); }
.comparison-card h4 { font-family: var(--font-display); font-size: 1rem; margin-bottom: 0.8rem; color: var(--primary-soft); }
.comparison-card ul { padding-left: 1.2rem; margin: 0; }
.comparison-card li { font-size: 0.85rem; color: var(--text-soft); line-height: 1.7; margin-bottom: 0.25rem; }

/* ── Info box (callout for supplemental info) ───────────────── */
.info-box {
  background: color-mix(in srgb, var(--primary) 8%, var(--surface));
  border: 1px solid color-mix(in srgb, var(--primary) 30%, var(--border));
  border-radius: var(--radius); padding: 1.2rem 1.5rem; margin: 1.4rem 0 2rem;
}
.info-box h4 { font-size: 0.95rem; font-weight: 600; color: var(--primary-soft); margin-bottom: 0.4rem; }
.info-box p  { font-size: 0.87rem; color: var(--text-soft); line-height: 1.7; margin: 0; }

/* ── Reading links ──────────────────────────────────────────── */
.reading-links {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(240px,1fr));
  gap: 0.85rem; margin: 1rem 0 2rem;
}
.reading-link {
  display: block; padding: 0.85rem 1rem;
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius-sm); color: var(--text-soft); font-size: 0.9rem;
  transition: border-color var(--transition), color var(--transition), transform 0.2s ease;
}
.reading-link:hover { border-color: var(--primary-soft); color: var(--primary-soft); transform: translateY(-2px); }

/* ── Modal ──────────────────────────────────────────────────── */
.modal-overlay {
  display: none; position: fixed; inset: 0; z-index: 2000;
  background: rgba(5,3,14,0.85); backdrop-filter: blur(8px);
  align-items: center; justify-content: center;
}
.modal-overlay.open { display: flex; animation: fadeIn 0.25s ease; }
.modal {
  background: var(--surface); border: 1px solid var(--border-hi);
  border-radius: var(--radius-lg); padding: 1.6rem;
  width: min(580px, 92vw); max-height: 80vh;
  overflow: auto; box-shadow: var(--shadow-lg);
  animation: scaleIn 0.25s ease;
}
.modal-header { display: flex; align-items: center; justify-content: space-between; margin-bottom: 1rem; }
.modal-header h3 { font-size: 1.1rem; }
.modal-close {
  width: 30px; height: 30px; border-radius: 6px;
  background: var(--surface-2); border: 1px solid var(--border);
  color: var(--text-soft); cursor: pointer; font-size: 0.9rem;
  display: flex; align-items: center; justify-content: center;
  transition: background var(--transition);
}
.modal-close:hover { background: var(--error); color: #fff; }
.modal pre {
  font-family: var(--font-mono); font-size: 0.82rem;
  background: #08051a; padding: 1rem; border-radius: var(--radius-sm);
  overflow-x: auto; line-height: 1.65; color: var(--text-soft);
}

/* ── Topic nav (prev/next) ──────────────────────────────────── */
.topic-nav {
  display: flex; justify-content: space-between; gap: 1rem;
  margin: 3rem 0 1.5rem; padding-top: 1.8rem;
  border-top: 1px solid var(--border);
}
.topic-nav-link {
  display: flex; align-items: center; gap: 0.85rem;
  padding: 0.9rem 1.2rem;
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); color: var(--text);
  min-width: 140px; max-width: 260px;
  transition: border-color var(--transition), box-shadow var(--transition), transform 0.2s ease;
}
.topic-nav-link:hover {
  border-color: var(--primary-soft);
  box-shadow: 0 4px 18px rgba(124,58,237,0.18);
  transform: translateY(-2px); color: var(--text);
}
.topic-nav-link.next { margin-left: auto; flex-direction: row-reverse; text-align: right; }
.topic-nav-arrow { font-size: 1.1rem; color: var(--primary-soft); }
.topic-nav-label {
  font-family: var(--font-mono); font-size: 0.68rem; letter-spacing: 0.12em;
  text-transform: uppercase; color: var(--primary-soft);
}
.topic-nav-title { font-size: 0.94rem; font-weight: 600; color: var(--text); }

/* ── HOME: Hero ─────────────────────────────────────────────── */
.hero {
  position: relative; min-height: 100vh; overflow: hidden;
  display: grid; grid-template-columns: 1fr 1fr; align-items: center;
  background: radial-gradient(ellipse 900px 600px at 20% 50%, rgba(124,58,237,0.16) 0%, transparent 65%), var(--bg);
  padding-top: 5rem;
}
.hero-inner {
  position: relative; z-index: 2;
  padding: 4rem clamp(1.5rem,3vw,3rem) 4rem clamp(1.5rem,5vw,5rem);
}
.hero-badge {
  display: inline-flex; align-items: center; gap: 0.4rem;
  background: var(--primary-faint); border: 1px solid rgba(124,58,237,0.35);
  border-radius: 999px; padding: 0.3rem 0.85rem;
  font-family: var(--font-mono); font-size: 0.72rem; letter-spacing: 0.1em;
  color: var(--primary-soft); margin-bottom: 1.4rem;
}
.hero-badge-dot {
  width: 6px; height: 6px; border-radius: 50%;
  background: var(--primary-soft); animation: pulse 2s ease-in-out infinite;
}
.hero h1 {
  font-family: var(--font-display);
  font-size: clamp(2.4rem, 5vw, 3.8rem);
  font-weight: 900; line-height: 1.08; color: var(--text); margin-bottom: 1.2rem;
}
.hero h1 em { font-style: italic; color: var(--primary-soft); }
.hero-sub {
  font-size: 1.05rem; color: var(--text-soft); line-height: 1.7;
  max-width: 50ch; margin-bottom: 2rem;
}
.hero-ctas { display: flex; gap: 0.85rem; flex-wrap: wrap; margin-bottom: 2.5rem; }
.btn-primary {
  padding: 0.75rem 1.8rem; border-radius: var(--radius-sm);
  background: var(--primary); color: #fff; font-weight: 600; font-size: 0.94rem;
  border: 1px solid var(--primary); cursor: pointer;
  transition: background var(--transition), box-shadow var(--transition), transform 0.2s ease;
}
.btn-primary:hover { background: #6d28d9; box-shadow: 0 0 20px rgba(124,58,237,0.5); transform: translateY(-2px); color: #fff; }
.btn-outline {
  padding: 0.75rem 1.6rem; border-radius: var(--radius-sm);
  background: transparent; color: var(--text-soft); font-weight: 500; font-size: 0.94rem;
  border: 1px solid var(--border); cursor: pointer;
  transition: border-color var(--transition), color var(--transition), transform 0.2s ease;
}
.btn-outline:hover { border-color: var(--primary-soft); color: var(--primary-soft); transform: translateY(-2px); }
.hero-stats { display: flex; gap: 2.2rem; flex-wrap: wrap; }
.hero-stat-val {
  font-family: var(--font-display); font-size: 2rem; font-weight: 700;
  color: var(--text); line-height: 1;
}
.hero-stat-label {
  font-family: var(--font-mono); font-size: 0.7rem; letter-spacing: 0.1em;
  text-transform: uppercase; color: var(--text-muted);
}
.hero-3d-panel {
  position: relative; height: 100%; min-height: 100vh; overflow: hidden;
}
#hero-canvas {
  position: absolute; inset: 0; width: 100%; height: 100%;
  -webkit-mask-image: linear-gradient(to right, transparent 0%, rgba(0,0,0,0.5) 12%, black 30%);
  mask-image: linear-gradient(to right, transparent 0%, rgba(0,0,0,0.5) 12%, black 30%);
}

/* CSS orb fallback (always rendered behind the canvas) */
.hero-orbs { position: absolute; inset: 0; pointer-events: none; }
.hero-orb {
  position: absolute; border-radius: 50%;
  filter: blur(70px); opacity: 0.35;
}
.orb-1 {
  width: 420px; height: 420px;
  background: radial-gradient(circle, #7C3AED 0%, transparent 70%);
  top: 10%; left: 20%;
  animation: orbFloat1 8s ease-in-out infinite;
}
.orb-2 {
  width: 320px; height: 320px;
  background: radial-gradient(circle, #06B6D4 0%, transparent 70%);
  bottom: 20%; right: 15%;
  animation: orbFloat2 11s ease-in-out infinite;
}
.orb-3 {
  width: 260px; height: 260px;
  background: radial-gradient(circle, #A78BFA 0%, transparent 70%);
  top: 50%; left: 50%;
  animation: orbFloat3 9s ease-in-out infinite;
}
@keyframes orbFloat1 { 0%,100%{transform:translate(0,0) scale(1)} 50%{transform:translate(-30px,40px) scale(1.1)} }
@keyframes orbFloat2 { 0%,100%{transform:translate(0,0) scale(1)} 50%{transform:translate(20px,-30px) scale(0.9)} }
@keyframes orbFloat3 { 0%,100%{transform:translate(-50%,-50%) scale(1)} 50%{transform:translate(-50%,-50%) scale(1.15)} }
.scroll-hint {
  position: absolute; bottom: 2rem; left: 50%; transform: translateX(-50%);
  display: flex; flex-direction: column; align-items: center; gap: 0.3rem;
  font-family: var(--font-mono); font-size: 0.65rem; letter-spacing: 0.2em;
  text-transform: uppercase; color: var(--text-muted); z-index: 5;
  animation: bounceY 2s ease-in-out infinite;
}
.scroll-hint::after { content: 'v'; font-size: 0.9rem; }

/* ── HOME: Stats bar ────────────────────────────────────────── */
.stats-bar {
  display: flex; justify-content: center; flex-wrap: wrap; gap: 0;
  border-top: 1px solid var(--border); border-bottom: 1px solid var(--border);
  background: var(--surface);
}
.stat-item {
  flex: 1; min-width: 120px;
  display: flex; flex-direction: column; align-items: center; justify-content: center;
  padding: 1.6rem 1rem; gap: 0.3rem;
  border-right: 1px solid var(--border);
}
.stat-item:last-child { border-right: none; }
.stat-num {
  font-family: var(--font-display); font-size: 2rem; font-weight: 700;
  color: var(--primary-soft); line-height: 1;
}
.stat-txt {
  font-family: var(--font-mono); font-size: 0.68rem; letter-spacing: 0.12em;
  text-transform: uppercase; color: var(--text-muted); text-align: center;
}

/* ── HOME: Curriculum section ───────────────────────────────── */
.curriculum-section {
  max-width: 1180px; margin: 0 auto; padding: 4rem 1.5rem 5rem;
}
.curriculum-label {
  font-family: var(--font-mono); font-size: 0.68rem; font-weight: 700;
  letter-spacing: 0.22em; text-transform: uppercase;
  color: var(--primary-soft); margin-bottom: 0.5rem;
}
.curriculum-title {
  font-family: var(--font-display); font-size: clamp(1.6rem, 3vw, 2.2rem);
  font-weight: 700; margin-bottom: 0.6rem;
}
.curriculum-sub { color: var(--text-soft); font-size: 1rem; margin-bottom: 2.5rem; max-width: 56ch; }

/* ── HOME: Course grid ──────────────────────────────────────── */
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px,1fr));
  gap: 1.1rem;
}
.course-card {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius-lg); padding: 1.5rem 1.6rem;
  position: relative; overflow: hidden;
  transition: border-color var(--transition), box-shadow var(--transition), transform 0.25s ease;
  text-decoration: none; color: var(--text); display: block;
}
.course-card::before {
  content: ''; position: absolute; top: 0; left: 0; right: 0; height: 3px;
  background: var(--card-color, var(--primary));
  opacity: 0; transition: opacity var(--transition);
}
.course-card::after {
  content: ''; position: absolute; inset: 0;
  background: radial-gradient(ellipse 200px 200px at 90% 20%, color-mix(in srgb, var(--card-color, var(--primary)) 8%, transparent) 0%, transparent 70%);
  pointer-events: none; opacity: 0; transition: opacity var(--transition);
}
.course-card:hover {
  border-color: color-mix(in srgb, var(--card-color, var(--primary)) 55%, transparent);
  box-shadow: 0 8px 32px color-mix(in srgb, var(--card-color, var(--primary)) 22%, transparent);
  transform: translateY(-4px); color: var(--text);
}
.course-card:hover::before { opacity: 1; }
.course-card:hover::after  { opacity: 1; }
.card-num {
  font-family: var(--font-mono); font-size: 0.68rem; letter-spacing: 0.16em;
  color: color-mix(in srgb, var(--card-color, var(--primary-soft)) 80%, var(--text-muted));
  font-weight: 700; margin-bottom: 0.65rem; text-transform: uppercase;
}
.card-title { font-size: 1.05rem; font-weight: 700; margin-bottom: 0.45rem; }
.card-desc { font-size: 0.86rem; color: var(--text-soft); line-height: 1.6; margin-bottom: 1rem; }
.card-meta { display: flex; gap: 0.5rem; flex-wrap: wrap; }
.card-tag {
  font-family: var(--font-mono); font-size: 0.68rem; letter-spacing: 0.06em;
  padding: 0.2rem 0.6rem; border-radius: 999px;
  background: var(--surface-2); border: 1px solid var(--border); color: var(--text-muted);
}

/* ── HOME: Footer ───────────────────────────────────────────── */
.site-footer {
  border-top: 1px solid var(--border); background: var(--surface);
  padding: 2.5rem 1.5rem; text-align: center;
}
.footer-brand { font-family: var(--font-head); font-size: 1.1rem; font-weight: 700; margin-bottom: 0.4rem; }
.footer-sub { font-size: 0.86rem; color: var(--text-muted); }
.footer-links { display: flex; gap: 1.5rem; justify-content: center; margin-top: 1rem; }
.footer-links a { font-size: 0.84rem; color: var(--text-muted); transition: color var(--transition); }
.footer-links a:hover { color: var(--primary-soft); }

/* ── Animations ─────────────────────────────────────────────── */
@keyframes fadeIn  { from { opacity: 0; } to { opacity: 1; } }
@keyframes fadeUp  { from { opacity: 0; transform: translateY(12px); } to { opacity: 1; transform: none; } }
@keyframes scaleIn { from { opacity: 0; transform: scale(0.94); } to { opacity: 1; transform: none; } }
@keyframes pulse   { 0%,100% { opacity: 1; } 50% { opacity: 0.4; } }
@keyframes glow    { 0%,100% { text-shadow: 0 0 8px rgba(124,58,237,0.6); } 50% { text-shadow: 0 0 16px rgba(124,58,237,1); } }
@keyframes bounceY { 0%,100% { transform: translateX(-50%) translateY(0); } 50% { transform: translateX(-50%) translateY(6px); } }

/* ── Responsive ─────────────────────────────────────────────── */
@media (max-width: 900px) {
  .hero { grid-template-columns: 1fr; }
  .hero-3d-panel { height: 55vw; min-height: 240px; max-height: 380px; }
  #hero-canvas {
    -webkit-mask-image: linear-gradient(to bottom, black 50%, transparent 100%);
    mask-image: linear-gradient(to bottom, black 50%, transparent 100%);
    opacity: 0.7;
  }
  .hero-inner { padding: 3rem 1.5rem 2rem; text-align: center; }
  .hero-ctas { justify-content: center; }
  .hero-stats { justify-content: center; }
}
@media (max-width: 640px) {
  .mini-cards { grid-template-columns: 1fr 1fr; }
  .course-grid { grid-template-columns: 1fr; }
  .topic-nav { flex-direction: column; }
  .topic-nav-link.next { margin-left: 0; text-align: left; flex-direction: row; }
  .stats-bar { flex-wrap: wrap; }
  .stat-item { min-width: 50%; border-right: none; border-bottom: 1px solid var(--border); }
  .reading-links { grid-template-columns: 1fr; }
  .curriculum-section { padding: 3rem 1.2rem; }
}
@media (max-width: 420px) {
  .navbar-links { display: none; }
  .mini-cards { grid-template-columns: 1fr; }
}