/* ══════════════════════════════════════════════════════════════════
   DevCraft Pro – style.css
   Dark-Theme Professional Design System
   ══════════════════════════════════════════════════════════════════ */

/* ── Design Tokens ────────────────────────────────────────────── */
:root {
  /* Backgrounds */
  --bg-base:     #0F1117;
  --bg-surface:  #1A1D27;
  --bg-elevated: #22263A;
  --bg-code:     #0D1117;

  /* Text */
  --text-primary:   #F0F2F8;
  --text-secondary: #9CA3AF;
  --text-tertiary:  #6B7280;
  --text-accent:    #A5B4FC;

  /* Borders */
  --border-subtle:  rgba(255,255,255,0.06);
  --border-default: rgba(255,255,255,0.12);
  --border-strong:  rgba(255,255,255,0.24);

  /* Brand */
  --brand:        #6366F1;
  --brand-hover:  #818CF8;

  /* Status */
  --success: #10B981;
  --warning: #F59E0B;
  --error:   #EF4444;
  --info:    #06B6D4;

  /* Spacing (8px base) */
  --sp-1: 4px;  --sp-2: 8px;   --sp-3: 12px; --sp-4: 16px;
  --sp-5: 20px; --sp-6: 24px;  --sp-8: 32px; --sp-10: 40px;
  --sp-12: 48px; --sp-16: 64px;

  /* Radius */
  --r-sm: 6px; --r-md: 10px; --r-lg: 16px; --r-xl: 24px;

  /* Typography */
  --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Consolas', monospace;

  /* Transitions */
  --t-fast:   150ms ease;
  --t-normal: 250ms ease;
  --t-slow:   400ms cubic-bezier(0.4, 0, 0.2, 1);
}

/* ── Reset & Base ─────────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-sans);
  background: var(--bg-base);
  color: var(--text-primary);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  overflow-x: hidden;
}

a { color: var(--text-accent); text-decoration: none; }
a:hover { color: var(--brand-hover); }

ul { list-style: none; }

img, svg { display: block; max-width: 100%; }

button {
  font-family: var(--font-sans);
  cursor: pointer;
  border: none;
  background: none;
}

:focus-visible {
  outline: 2px solid var(--brand);
  outline-offset: 3px;
  border-radius: var(--r-sm);
}

/* ── Icon Sizing ──────────────────────────────────────────────── */
.icon { width: 18px; height: 18px; display: inline-block; vertical-align: middle; flex-shrink: 0; }
.icon-lg { width: 28px; height: 28px; }
.icon-xl { width: 48px; height: 48px; }

/* ── Scrollbar ────────────────────────────────────────────────── */
::-webkit-scrollbar { width: 8px; height: 8px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border-strong); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: rgba(255,255,255,0.35); }

/* ══════════════════════════════════════════════════════════════════
   HEADER
   ══════════════════════════════════════════════════════════════════ */
.app-header {
  position: sticky;
  top: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  gap: var(--sp-4);
  padding: 0 var(--sp-6);
  height: 60px;
  background: rgba(15, 17, 23, 0.9);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border-subtle);
}

/* Brand */
.brand {
  display: flex;
  align-items: center;
  gap: var(--sp-2);
  color: var(--text-primary);
  text-decoration: none;
  flex-shrink: 0;
}
.brand:hover { color: var(--brand-hover); }
.brand-logo { width: 32px; height: 32px; color: var(--brand); }
.brand-name {
  font-size: 1.1rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}
.badge-pro {
  font-size: 0.65rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: #ec4899;
  background-color: rgba(236, 72, 153, 0.12);
  border: 1px solid rgba(236, 72, 153, 0.35);
  border-radius: var(--r-sm);
  padding: 0.15em 0.45em;
  line-height: 1;
  align-self: center;
}

/* Breadcrumb */
.breadcrumb {
  display: flex;
  align-items: center;
  gap: var(--sp-1);
  flex: 1;
  min-width: 0;
  overflow: hidden;
}
.breadcrumb-item {
  color: var(--text-secondary);
  font-size: 0.875rem;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  transition: color var(--t-fast);
}
.breadcrumb-item:hover { color: var(--text-primary); }
.breadcrumb-item.current { color: var(--text-primary); font-weight: 500; pointer-events: none; }
.breadcrumb-sep { color: var(--text-tertiary); font-size: 0.875rem; }

/* Search */
.search-container {
  position: relative;
  flex-shrink: 0;
  width: 260px;
}
.search-input-wrap {
  position: relative;
  display: flex;
  align-items: center;
}
.search-icon {
  position: absolute;
  left: var(--sp-3);
  color: var(--text-tertiary);
  pointer-events: none;
}
.search-input {
  width: 100%;
  padding: var(--sp-2) var(--sp-3) var(--sp-2) calc(var(--sp-3) + 18px + var(--sp-2));
  background: var(--bg-elevated);
  border: 1px solid var(--border-default);
  border-radius: var(--r-md);
  color: var(--text-primary);
  font-size: 0.875rem;
  font-family: var(--font-sans);
  transition: border-color var(--t-fast), background var(--t-fast);
}
.search-input::placeholder { color: var(--text-tertiary); }
.search-input:focus {
  outline: none;
  border-color: var(--brand);
  background: var(--bg-surface);
}
.search-input::-webkit-search-cancel-button { display: none; }

/* Search Dropdown */
.search-dropdown {
  position: absolute;
  top: calc(100% + var(--sp-2));
  left: 0;
  right: 0;
  background: var(--bg-elevated);
  border: 1px solid var(--border-default);
  border-radius: var(--r-md);
  overflow: hidden;
  box-shadow: 0 16px 48px rgba(0,0,0,0.5);
  z-index: 200;
}
.search-result-item {
  display: flex;
  flex-direction: column;
  gap: 2px;
  padding: var(--sp-3) var(--sp-4);
  transition: background var(--t-fast);
  cursor: pointer;
}
.search-result-item:hover { background: rgba(255,255,255,0.06); }
.result-type {
  font-size: 0.7rem;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-tertiary);
}
.result-title { font-size: 0.875rem; color: var(--text-primary); }
.search-empty {
  padding: var(--sp-4);
  color: var(--text-secondary);
  font-size: 0.875rem;
  text-align: center;
}

/* ══════════════════════════════════════════════════════════════════
   MAIN / FOOTER
   ══════════════════════════════════════════════════════════════════ */
.app-main {
  flex: 1;
  animation: fadeIn var(--t-normal) both;
}
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to   { opacity: 1; transform: translateY(0); }
}

.app-footer {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-3);
  padding: var(--sp-4) var(--sp-6);
  border-top: 1px solid var(--border-subtle);
  color: var(--text-tertiary);
  font-size: 0.8rem;
  flex-wrap: wrap;
}
.footer-brand { font-weight: 600; color: var(--text-secondary); }
.footer-sep { opacity: 0.4; }

/* ══════════════════════════════════════════════════════════════════
   LOADING STATE
   ══════════════════════════════════════════════════════════════════ */
.loading-screen {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 60vh;
  gap: var(--sp-4);
  color: var(--text-secondary);
}
.loading-spinner {
  width: 36px;
  height: 36px;
  border: 3px solid var(--border-default);
  border-top-color: var(--brand);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* ══════════════════════════════════════════════════════════════════
   HOME VIEW – HERO
   ══════════════════════════════════════════════════════════════════ */
.hero {
  text-align: center;
  padding: var(--sp-16) var(--sp-6) var(--sp-10);
  max-width: 680px;
  margin: 0 auto;
}
.hero-badge {
  display: inline-block;
  padding: var(--sp-1) var(--sp-3);
  background: rgba(99,102,241,0.15);
  border: 1px solid rgba(99,102,241,0.3);
  border-radius: 100px;
  font-size: 0.75rem;
  font-weight: 500;
  color: var(--text-accent);
  letter-spacing: 0.05em;
  text-transform: uppercase;
  margin-bottom: var(--sp-5);
}
.hero-title {
  font-size: clamp(2rem, 5vw, 3.5rem);
  font-weight: 800;
  line-height: 1.1;
  letter-spacing: -0.03em;
  margin-bottom: var(--sp-4);
}
.gradient-text {
  background: linear-gradient(135deg, #818CF8 0%, #A78BFA 50%, #60A5FA 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.hero-subtitle {
  font-size: 1.125rem;
  color: var(--text-secondary);
  line-height: 1.6;
  margin-bottom: var(--sp-6);
}
.hero-stats {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-3);
  font-size: 0.875rem;
  color: var(--text-tertiary);
}
.hero-stats .divider { opacity: 0.4; }

/* ══════════════════════════════════════════════════════════════════
   TOPIC GRID (Home)
   ══════════════════════════════════════════════════════════════════ */
.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: var(--sp-5);
  padding: 0 var(--sp-6) var(--sp-16);
  max-width: 1280px;
  margin: 0 auto;
}

/* ── Topic Card ───────────────────────────────────────────────── */
.topic-card {
  position: relative;
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  border-radius: var(--r-lg);
  overflow: hidden;
  cursor: pointer;
  transition: transform var(--t-normal), box-shadow var(--t-normal), border-color var(--t-normal);
  display: flex;
  flex-direction: column;
}
.topic-card:hover {
  transform: translateY(-4px);
  border-color: color-mix(in srgb, var(--topic-color) 40%, transparent);
  box-shadow:
    0 12px 40px rgba(0,0,0,0.4),
    0 0 0 1px color-mix(in srgb, var(--topic-color) 20%, transparent),
    0 4px 24px color-mix(in srgb, var(--topic-color) 15%, transparent);
}
.topic-card:focus-visible {
  outline: 2px solid var(--topic-color);
  outline-offset: 2px;
}

.card-accent-bar {
  height: 3px;
  background: var(--topic-color);
  flex-shrink: 0;
}

.card-header {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  padding: var(--sp-5) var(--sp-5) var(--sp-3);
}
.card-icon { color: var(--topic-color); flex-shrink: 0; }
.card-icon svg { width: 24px; height: 24px; }
.card-title { font-size: 1.1rem; font-weight: 700; line-height: 1.3; }

.card-tagline {
  font-size: 0.875rem;
  color: var(--text-secondary);
  padding: 0 var(--sp-5) var(--sp-4);
  line-height: 1.5;
  flex: 1;
}

.card-subareas {
  display: flex;
  flex-wrap: wrap;
  gap: var(--sp-2);
  padding: 0 var(--sp-5) var(--sp-4);
}
.subarea-chip {
  font-size: 0.7rem;
  font-weight: 500;
  padding: 3px var(--sp-2);
  background: rgba(255,255,255,0.06);
  border: 1px solid var(--border-subtle);
  border-radius: 100px;
  color: var(--text-secondary);
  white-space: nowrap;
}
.subarea-chip.more { color: var(--text-tertiary); }

.card-footer {
  padding: var(--sp-3) var(--sp-5) var(--sp-5);
  border-top: 1px solid var(--border-subtle);
  margin-top: auto;
}
.card-cta {
  display: flex;
  align-items: center;
  gap: var(--sp-2);
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--topic-color);
  transition: gap var(--t-fast);
}
.topic-card:hover .card-cta { gap: var(--sp-3); }

/* ══════════════════════════════════════════════════════════════════
   TOPIC VIEW (Level 2)
   ══════════════════════════════════════════════════════════════════ */

/* Hero Banner */
.topic-hero {
  padding: var(--sp-12) var(--sp-6) var(--sp-10);
  margin-bottom: var(--sp-8);
}
.topic-hero-inner {
  max-width: 900px;
  margin: 0 auto;
  display: flex;
  align-items: flex-start;
  gap: var(--sp-6);
}
.topic-hero-icon {
  width: 72px;
  height: 72px;
  background: rgba(255,255,255,0.15);
  border-radius: var(--r-lg);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  backdrop-filter: blur(8px);
}
.topic-hero-icon svg { width: 40px; height: 40px; color: white; }

.topic-hero-text { flex: 1; }
.topic-hero-title {
  font-size: clamp(1.75rem, 3vw, 2.5rem);
  font-weight: 800;
  letter-spacing: -0.025em;
  color: white;
  margin-bottom: var(--sp-2);
  text-shadow: 0 2px 8px rgba(0,0,0,0.3);
}
.topic-hero-tagline {
  font-size: 1.05rem;
  color: rgba(255,255,255,0.8);
  line-height: 1.5;
  margin-bottom: var(--sp-4);
}
.topic-hero-meta {
  display: flex;
  align-items: center;
  gap: var(--sp-4);
  flex-wrap: wrap;
}
.topic-hero-meta span { font-size: 0.875rem; color: rgba(255,255,255,0.65); }
.related-link {
  color: rgba(255,255,255,0.9);
  text-decoration: underline;
  text-underline-offset: 3px;
}
.related-link:hover { color: white; }

/* Overview */
.topic-overview {
  max-width: 720px;
  margin: 0 auto var(--sp-8);
  padding: 0 var(--sp-6);
  color: var(--text-secondary);
  font-size: 1rem;
  line-height: 1.75;
}

/* Subareas Grid */
.subareas-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(560px, 1fr));
  gap: var(--sp-5);
  max-width: 1280px;
  margin: 0 auto;
  padding: 0 var(--sp-6) var(--sp-16);
}

/* ── Subarea Card ─────────────────────────────────────────────── */
.subarea-card {
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  border-radius: var(--r-lg);
  overflow: hidden;
  transition: border-color var(--t-normal);
}
.subarea-card.expanded {
  border-color: color-mix(in srgb, var(--topic-color) 30%, transparent);
}

.subarea-main { padding: var(--sp-5); }

.subarea-header {
  display: flex;
  align-items: flex-start;
  gap: var(--sp-3);
  margin-bottom: var(--sp-3);
}
.subarea-icon { color: var(--topic-color); flex-shrink: 0; margin-top: 2px; }
.subarea-icon svg { width: 20px; height: 20px; }
.subarea-title { font-size: 1.05rem; font-weight: 700; flex: 1; line-height: 1.3; }

.deep-dive-toggle {
  display: flex;
  align-items: center;
  gap: var(--sp-1);
  padding: var(--sp-1) var(--sp-3);
  background: rgba(255,255,255,0.06);
  border: 1px solid var(--border-default);
  border-radius: 100px;
  font-size: 0.75rem;
  font-weight: 500;
  color: var(--text-secondary);
  transition: background var(--t-fast), color var(--t-fast), border-color var(--t-fast);
  white-space: nowrap;
  flex-shrink: 0;
}
.deep-dive-toggle:hover {
  background: color-mix(in srgb, var(--topic-color) 15%, transparent);
  border-color: color-mix(in srgb, var(--topic-color) 40%, transparent);
  color: var(--topic-color);
}
.subarea-card.expanded .deep-dive-toggle {
  background: color-mix(in srgb, var(--topic-color) 20%, transparent);
  border-color: var(--topic-color);
  color: var(--topic-color);
}

.subarea-concept {
  font-size: 0.9rem;
  color: var(--text-accent);
  margin-bottom: var(--sp-3);
  line-height: 1.5;
  padding-left: calc(20px + var(--sp-3));
}

.subarea-body {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.75;
  margin-bottom: var(--sp-4);
  padding-left: calc(20px + var(--sp-3));
}

.subarea-meta {
  display: flex;
  flex-direction: column;
  gap: var(--sp-4);
}

/* Key Points */
.key-points h4, .tools-section h4, .commands-section h4 {
  font-size: 0.7rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--text-tertiary);
  margin-bottom: var(--sp-2);
}
.key-points ul { display: flex; flex-direction: column; gap: var(--sp-2); }
.key-points li {
  font-size: 0.875rem;
  color: var(--text-secondary);
  padding-left: var(--sp-4);
  position: relative;
  line-height: 1.55;
}
.key-points li::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0.6em;
  width: 5px;
  height: 5px;
  background: var(--topic-color);
  border-radius: 50%;
  opacity: 0.7;
}

/* Tools */
.tool-list { display: flex; flex-direction: column; gap: var(--sp-2); }
.tool-item {
  display: flex;
  gap: var(--sp-3);
  align-items: baseline;
  font-size: 0.8rem;
}
.tool-name {
  font-weight: 600;
  color: var(--text-primary);
  background: rgba(255,255,255,0.06);
  padding: 2px 8px;
  border-radius: var(--r-sm);
  white-space: nowrap;
  font-size: 0.75rem;
  flex-shrink: 0;
}
.tool-purpose { color: var(--text-secondary); line-height: 1.4; }

/* Commands */
.commands-section { display: flex; flex-direction: column; gap: var(--sp-2); }
.command-row {
  display: flex;
  flex-direction: column;
  gap: 2px;
}
.command-code {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--text-accent);
  background: var(--bg-code);
  padding: var(--sp-2) var(--sp-3);
  border-radius: var(--r-sm);
  display: block;
  overflow-x: auto;
  white-space: nowrap;
  border: 1px solid var(--border-subtle);
}
.command-desc {
  font-size: 0.78rem;
  color: var(--text-tertiary);
  padding-left: var(--sp-3);
}

/* ══════════════════════════════════════════════════════════════════
   DEEP DIVE PANEL (Level 3)
   ══════════════════════════════════════════════════════════════════ */
.deep-dive-panel {
  border-top: 1px solid var(--border-default);
  background: color-mix(in srgb, var(--topic-color) 4%, var(--bg-code));
  overflow: hidden;
}

.deep-dive-header {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  padding: var(--sp-5) var(--sp-5) var(--sp-4);
  border-bottom: 1px solid var(--border-subtle);
}
.deep-dive-header h3 {
  font-size: 1rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: var(--sp-2);
  color: var(--topic-color);
}
.deep-dive-header svg { width: 16px; height: 16px; }

.deep-dive-intro {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.7;
  padding: var(--sp-4) var(--sp-5);
}

.dd-section {
  padding: 0 var(--sp-5) var(--sp-5);
}
.dd-section h4 {
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: var(--sp-2);
  padding-bottom: var(--sp-2);
  border-bottom: 1px solid var(--border-subtle);
}
.dd-section p {
  font-size: 0.875rem;
  color: var(--text-secondary);
  line-height: 1.75;
  margin-bottom: var(--sp-3);
}

/* Code Block */
.code-block {
  background: var(--bg-code);
  border: 1px solid var(--border-default);
  border-radius: var(--r-md);
  overflow: hidden;
  margin: var(--sp-3) 0;
}
.code-header {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  padding: var(--sp-2) var(--sp-4);
  background: rgba(255,255,255,0.03);
  border-bottom: 1px solid var(--border-subtle);
}
.code-lang {
  font-size: 0.7rem;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-tertiary);
  background: rgba(255,255,255,0.07);
  padding: 2px 8px;
  border-radius: 4px;
}
.code-label {
  font-size: 0.8rem;
  color: var(--text-secondary);
  flex: 1;
}
.copy-btn {
  display: flex;
  align-items: center;
  gap: var(--sp-1);
  font-size: 0.75rem;
  font-weight: 500;
  color: var(--text-tertiary);
  padding: var(--sp-1) var(--sp-2);
  border-radius: var(--r-sm);
  transition: color var(--t-fast), background var(--t-fast);
}
.copy-btn svg { width: 13px; height: 13px; }
.copy-btn:hover { color: var(--text-primary); background: rgba(255,255,255,0.07); }
.copy-btn.copied { color: var(--success); }

.code-pre {
  margin: 0;
  padding: var(--sp-4);
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 0.82rem;
  line-height: 1.65;
  color: #e2e8f0;
  tab-size: 2;
}
.code-pre code { font-family: inherit; background: none; }

/* ASCII Diagram */
.ascii-diagram {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--text-secondary);
  background: rgba(255,255,255,0.03);
  border: 1px solid var(--border-subtle);
  border-radius: var(--r-sm);
  padding: var(--sp-3) var(--sp-4);
  overflow-x: auto;
  margin: var(--sp-3) 0;
  line-height: 1.5;
}

/* Best Practices / Pitfalls */
.dd-columns {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--sp-4);
  padding: 0 var(--sp-5) var(--sp-5);
}
@media (max-width: 700px) { .dd-columns { grid-template-columns: 1fr; } }

.dd-best-practices, .dd-pitfalls {
  background: rgba(255,255,255,0.03);
  border-radius: var(--r-md);
  padding: var(--sp-4);
}
.dd-best-practices { border: 1px solid rgba(16,185,129,0.2); }
.dd-pitfalls       { border: 1px solid rgba(239,68,68,0.2); }

.dd-best-practices h4, .dd-pitfalls h4 {
  font-size: 0.8rem;
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: var(--sp-2);
  margin-bottom: var(--sp-3);
}
.dd-best-practices h4 { color: var(--success); }
.dd-pitfalls h4       { color: var(--error); }
.dd-best-practices h4 svg, .dd-pitfalls h4 svg { width: 14px; height: 14px; }

.dd-best-practices ul, .dd-pitfalls ul { display: flex; flex-direction: column; gap: var(--sp-2); }
.dd-best-practices li, .dd-pitfalls li {
  font-size: 0.82rem;
  line-height: 1.5;
  padding-left: var(--sp-3);
  position: relative;
}
.dd-best-practices li { color: rgba(16,185,129,0.9); }
.dd-pitfalls li       { color: rgba(239,68,68,0.9); }
.dd-best-practices li::before {
  content: '✓';
  position: absolute;
  left: 0;
  font-size: 0.7rem;
  color: var(--success);
}
.dd-pitfalls li::before {
  content: '✗';
  position: absolute;
  left: 0;
  font-size: 0.7rem;
  color: var(--error);
}

/* Further Reading */
.dd-reading {
  padding: 0 var(--sp-5) var(--sp-6);
}
.dd-reading h4 {
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--text-tertiary);
  display: flex;
  align-items: center;
  gap: var(--sp-2);
  margin-bottom: var(--sp-3);
}
.dd-reading h4 svg { width: 13px; height: 13px; }
.reading-links { display: flex; flex-wrap: wrap; gap: var(--sp-2); }
.reading-link {
  display: flex;
  align-items: center;
  gap: var(--sp-1);
  font-size: 0.8rem;
  color: var(--text-accent);
  padding: var(--sp-1) var(--sp-3);
  border: 1px solid rgba(165,180,252,0.2);
  border-radius: 100px;
  transition: background var(--t-fast), border-color var(--t-fast);
}
.reading-link svg { width: 12px; height: 12px; }
.reading-link:hover {
  background: rgba(165,180,252,0.1);
  border-color: rgba(165,180,252,0.4);
  color: var(--brand-hover);
}

/* ══════════════════════════════════════════════════════════════════
   ERROR & EMPTY STATES
   ══════════════════════════════════════════════════════════════════ */
.error-view {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 50vh;
  gap: var(--sp-4);
  color: var(--text-secondary);
  text-align: center;
  padding: var(--sp-8);
}
.error-view h2 { font-size: 1.5rem; color: var(--text-primary); }
.error-view a {
  padding: var(--sp-2) var(--sp-5);
  background: var(--brand);
  color: white;
  border-radius: var(--r-md);
  font-weight: 500;
}
.error-view a:hover { background: var(--brand-hover); }

/* ══════════════════════════════════════════════════════════════════
   ACCESSIBILITY & MOTION
   ══════════════════════════════════════════════════════════════════ */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}

/* ══════════════════════════════════════════════════════════════════
   RESPONSIVE
   ══════════════════════════════════════════════════════════════════ */
@media (max-width: 900px) {
  .subareas-grid { grid-template-columns: 1fr; }
}

@media (max-width: 680px) {
  .app-header { padding: 0 var(--sp-4); gap: var(--sp-3); }
  .brand-name { display: none; }
  .breadcrumb { display: none; }
  .search-container { width: 200px; }
  .topic-grid { grid-template-columns: 1fr; padding: 0 var(--sp-4) var(--sp-10); }
  .hero { padding: var(--sp-10) var(--sp-4) var(--sp-8); }
  .topic-hero { padding: var(--sp-8) var(--sp-4) var(--sp-6); }
  .topic-hero-inner { flex-direction: column; gap: var(--sp-4); }
  .topic-hero-icon { width: 56px; height: 56px; }
  .topic-overview { padding: 0 var(--sp-4); }
  .subareas-grid { padding: 0 var(--sp-4) var(--sp-10); }
  .subarea-body { padding-left: 0; }
  .subarea-concept { padding-left: 0; }
}

/* ══════════════════════════════════════════════════════════════════
   UTILITY
   ══════════════════════════════════════════════════════════════════ */
.sr-only {
  position: absolute;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden;
  clip: rect(0,0,0,0);
  white-space: nowrap;
  border: 0;
}