/* ===== Design Tokens ===== */
:root {
  --color-bg: #f8f9fa;
  --color-surface: #ffffff;
  --color-border: #e5e7eb;
  --color-border-strong: #d1d5db;
  --color-text: #111827;
  --color-text-muted: #6b7280;
  --color-accent: #111827;
  --color-primary: #4f46e5;
  --color-primary-light: #ede9fe;
  --color-blue: #3b82f6;
  --color-purple: #7c3aed;
  --color-teal: #0d9488;
  --color-green: #22c55e;

  --cat-systemdesign: #4f46e5;
  --cat-beginner: #16a34a;
  --cat-advanced: #dc2626;

  --font-body: 'Inter', sans-serif;
  --font-display: 'Sora', sans-serif;
  --font-mono: 'ui-monospace', 'SFMono-Regular', 'Menlo', monospace;

  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-pill: 9999px;

  --shadow-sm: 0 1px 4px rgba(0, 0, 0, 0.06);
  --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.12);

  --transition: 0.18s ease;

  --content-max: 1280px;
  --sidebar-w: 260px;
}

/* ===== Reset ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; overflow-x: hidden; }
body {
  font-family: var(--font-body);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.75;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}
main { flex: 1; }
img, svg { max-width: 100%; display: block; }
a { color: var(--color-primary); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ===== Typography ===== */
h1 {
  font-family: var(--font-display);
  font-size: clamp(2.4rem, 5.5vw, 4rem);
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.1;
}
h2 {
  font-family: var(--font-display);
  font-size: clamp(1.6rem, 3.5vw, 2.4rem);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.2;
}
h3 { font-size: 1.1rem; font-weight: 600; line-height: 1.4; }
h4 { font-size: 0.95rem; font-weight: 600; }
p { margin-bottom: 1rem; }
ul, ol { margin-bottom: 1rem; padding-left: 1.5rem; }
li { margin-bottom: 0.35rem; }
code {
  font-family: var(--font-mono);
  font-size: 0.875em;
  background: #f3f4f6;
  padding: 0.15em 0.45em;
  border-radius: 4px;
  color: #374151;
}
pre {
  overflow-x: auto;
  max-width: 100%;
  background: #1e293b;
  border-radius: var(--radius-md);
  padding: 1.25rem;
  margin: 1.5rem 0;
  border: 1px solid #334155;
}
pre code {
  background: none;
  padding: 0;
  border-radius: 0;
  font-size: 0.875rem;
  line-height: 1.65;
  color: #e2e8f0;
  white-space: pre;
}

/* ===== Global Nav ===== */
.site-header {
  background: rgba(255, 255, 255, 0.6);
  position: sticky;
  top: 0;
  z-index: 100;
  border-bottom: 1px solid rgba(229, 231, 235, 0.6);
  box-shadow: 0 1px 20px rgba(0, 0, 0, 0.06);
  backdrop-filter: blur(16px) saturate(180%);
  -webkit-backdrop-filter: blur(16px) saturate(180%);
}
.nav-inner {
  max-width: var(--content-max);
  margin: 0 auto;
  padding: 0 1.5rem;
  height: 64px;
  display: flex;
  align-items: center;
  gap: 1.5rem;
  min-width: 0;
  overflow: hidden;
}
.nav-logo {
  font-family: var(--font-display);
  font-size: 1.25rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--color-text);
  text-decoration: none;
  white-space: nowrap;
  flex-shrink: 0;
}
.nav-logo span { color: var(--color-primary); }
.nav-logo:hover { text-decoration: none; }
.nav-links {
  display: flex;
  align-items: center;
  gap: 0.25rem;
  list-style: none;
  margin: 0;
  padding: 0;
  flex: 1;
}
.nav-links a {
  color: var(--color-text-muted);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
  padding: 0.4rem 0.85rem;
  border-radius: var(--radius-pill);
  transition: color var(--transition), background var(--transition);
}
.nav-links a:hover { color: var(--color-text); background: var(--color-bg); text-decoration: none; }
.nav-links a.active { color: var(--color-primary); background: var(--color-primary-light); }
.nav-chapters { list-style: none; padding: 0; margin: 0; display: flex; align-items: center; gap: 0.15rem; }
.nav-chapters li a { font-size: 0.82rem; font-weight: 500; color: var(--color-text-muted); text-decoration: none; padding: 0.3rem 0.6rem; border-radius: var(--radius-pill); transition: color var(--transition), background var(--transition); white-space: nowrap; }
.nav-chapters li a:hover { color: var(--color-text); background: var(--color-bg); }
.nav-actions { display: flex; align-items: center; gap: 0.75rem; margin-left: auto; flex-shrink: 0; }
.nav-progress {
  display: flex; align-items: center; gap: 0.5rem;
  color: var(--color-text-muted); font-size: 0.8rem; font-weight: 500;
  text-decoration: none; padding: 0.35rem 0.7rem;
  border-radius: var(--radius-pill);
  transition: background var(--transition), color var(--transition);
}
.nav-progress:hover { background: var(--color-bg); color: var(--color-text); text-decoration: none; }
.nav-progress-bar {
  width: 72px; height: 4px;
  background: var(--color-border); border-radius: 2px; overflow: hidden;
  flex-shrink: 0;
}
.nav-progress-fill {
  height: 100%; background: var(--color-primary);
  border-radius: 2px; transition: width 0.4s ease;
}
.btn-primary {
  background: var(--color-accent);
  color: #fff;
  padding: 0.5rem 1.2rem;
  border: none;
  border-radius: var(--radius-pill);
  font-family: var(--font-body);
  font-weight: 600;
  font-size: 0.875rem;
  text-decoration: none;
  transition: background var(--transition), box-shadow var(--transition), transform var(--transition);
  white-space: nowrap;
  box-shadow: var(--shadow-sm);
  cursor: pointer;
}
.btn-primary:hover { background: #1f2937; box-shadow: var(--shadow-md); transform: translateY(-1px); text-decoration: none; }

/* Nav CTA — glassmorphism */
#nav-cta {
  position: relative;
  overflow: hidden;
  background: linear-gradient(135deg, rgba(79,70,229,0.18) 0%, rgba(124,58,237,0.12) 100%);
  color: var(--color-primary);
  border: 1px solid rgba(124, 58, 237, 0.3);
  backdrop-filter: blur(16px) saturate(200%) brightness(1.05);
  -webkit-backdrop-filter: blur(16px) saturate(200%) brightness(1.05);
  box-shadow: 0 2px 16px rgba(79,70,229,0.15), inset 0 1px 0 rgba(255,255,255,0.18), inset 0 -1px 0 rgba(79,70,229,0.1);
}
#nav-cta::before {
  content: '';
  position: absolute;
  top: 0; left: -100%;
  width: 60%; height: 100%;
  background: linear-gradient(90deg, transparent, rgba(255,255,255,0.18), transparent);
  transition: left 0.55s ease;
  pointer-events: none;
}
#nav-cta:hover::before { left: 160%; }
#nav-cta:hover {
  background: linear-gradient(135deg, rgba(79,70,229,0.28) 0%, rgba(124,58,237,0.22) 100%);
  border-color: rgba(124,58,237,0.55);
  color: var(--color-primary);
  box-shadow: 0 4px 28px rgba(79,70,229,0.28), 0 0 0 3px rgba(79,70,229,0.08), inset 0 1px 0 rgba(255,255,255,0.25);
  transform: translateY(-1px);
}
.search-btn {
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  color: var(--color-text-muted);
  padding: 0.4rem 1rem;
  cursor: pointer;
  font-size: 0.85rem;
  font-family: var(--font-body);
  display: flex;
  align-items: center;
  gap: 0.4rem;
  transition: border-color var(--transition), color var(--transition), box-shadow var(--transition);
}
.search-btn:hover { border-color: var(--color-primary); color: var(--color-text); box-shadow: var(--shadow-sm); }

/* ===== Hero ===== */
.hero {
  border-bottom: 1px solid var(--color-border);
  color: var(--color-text);
  padding: 5rem 1.5rem 4rem;
}
.hero-inner {
  max-width: var(--content-max);
  margin: 0 auto;
  display: grid;
  grid-template-columns: 1fr 1.2fr;
  gap: 3rem;
  align-items: center;
}
.hero-left { display: flex; flex-direction: column; align-items: flex-start; }
.hero-right { display: flex; align-items: center; justify-content: center; }
.hero-diagram {
  width: 100%;
  max-width: 860px;
  border-radius: 1.5rem;
  overflow: hidden;
  background: var(--color-bg);
}
.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: var(--color-primary-light);
  border: none;
  border-radius: var(--radius-pill);
  color: var(--color-primary);
  font-size: 0.8rem;
  font-weight: 600;
  padding: 0.35rem 0.9rem;
  margin-bottom: 1.5rem;
  letter-spacing: 0.01em;
}
.hero h1 { color: var(--color-text); margin-bottom: 1.25rem; }
.hero h1 em { font-style: normal; color: var(--color-primary); }
.hero-sub { font-size: 1rem; color: var(--color-text-muted); max-width: 520px; margin-bottom: 2rem; line-height: 1.7; }
.hero-ctas { display: flex; gap: 0.75rem; flex-wrap: wrap; margin-bottom: 2.5rem; }
.btn-secondary {
  background: var(--color-surface);
  border: 1.5px solid var(--color-border-strong);
  border-radius: var(--radius-pill);
  color: var(--color-text);
  padding: 0.5rem 1.2rem;
  font-family: var(--font-body);
  font-weight: 600;
  font-size: 0.875rem;
  text-decoration: none;
  transition: border-color var(--transition), box-shadow var(--transition), transform var(--transition);
}
.btn-secondary:hover { border-color: var(--color-primary); box-shadow: var(--shadow-sm); transform: translateY(-1px); text-decoration: none; }
.btn-large { padding: 0.65rem 1.5rem; font-size: 0.95rem; }
.stats-bar {
  display: flex;
  gap: 2rem;
  flex-wrap: wrap;
}
.stat { display: flex; align-items: center; gap: 0.4rem; }
.stat-num { font-family: var(--font-display); font-size: 1.3rem; font-weight: 700; color: var(--color-text); }
.stat-label { font-size: 0.8rem; color: var(--color-text-muted); }

/* ===== Hero Diagram ===== */

/* ===== Section Layout ===== */
.section { padding: 4rem 1.5rem; }
.section-inner { max-width: var(--content-max); margin: 0 auto; }
.section-header { margin-bottom: 2.5rem; }
.section-header h2 { margin-bottom: 0.5rem; }
.section-header p { color: var(--color-text-muted); font-size: 1rem; }
.section-alt { background: var(--color-bg); }

/* ===== Tag Filter Bar ===== */
.tag-filter-bar {
  max-width: var(--content-max);
  margin: 0 auto;
  padding: 0.75rem 1.5rem;
  display: flex;
  align-items: center;
  gap: 0.75rem;
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  flex-wrap: wrap;
}
.tag-filter-active { font-size: 0.85rem; color: var(--color-text-muted); }
.tag-filter-active strong { color: var(--color-primary); }
.tag-filter-clear {
  font-size: 0.78rem;
  padding: 0.2rem 0.65rem;
  border-radius: 999px;
  border: 1px solid var(--color-border);
  background: none;
  cursor: pointer;
  color: var(--color-text-muted);
  transition: color var(--transition), border-color var(--transition);
}
.tag-filter-clear:hover { color: var(--color-text); border-color: var(--color-text-muted); }
.guide-card.hidden { display: none; }
.section.hidden { display: none; }

/* ===== Category Grid ===== */
.categories-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.25rem;
}
.cat-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 1.75rem;
  text-decoration: none;
  color: inherit;
  transition: transform var(--transition), box-shadow var(--transition), border-color var(--transition);
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  box-shadow: var(--shadow-sm);
}
.cat-card:hover { transform: translateY(-3px); box-shadow: var(--shadow-md); border-color: var(--color-primary); text-decoration: none; }
.cat-icon {
  width: 48px; height: 48px;
  border-radius: var(--radius-sm);
  background: var(--color-primary-light);
  display: flex; align-items: center; justify-content: center;
  font-size: 1.5rem;
}
.cat-card h3 { font-size: 1.05rem; }
.cat-card p { font-size: 0.875rem; color: var(--color-text-muted); margin: 0; }
.cat-count { font-size: 0.8rem; font-weight: 600; margin-top: auto; color: var(--color-primary); }

/* ===== Guide Grid ===== */
.guides-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.25rem;
}

/* ===== Footer ===== */
.site-footer {
  background: var(--color-surface);
  color: var(--color-text-muted);
  border-top: 1px solid var(--color-border);
  padding: 1.5rem 1.5rem;
  text-align: center;
}
.footer-inner { max-width: var(--content-max); margin: 0 auto; }
.footer-logo {
  font-family: var(--font-display);
  font-size: 1.25rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--color-text);
  margin-bottom: 0.5rem;
}
.footer-logo span { color: var(--color-primary); }
.footer-links { display: flex; justify-content: center; gap: 1.5rem; flex-wrap: wrap; margin: 0.5rem 0; list-style: none; }
.footer-links a { color: var(--color-text-muted); font-size: 0.875rem; }
.footer-links a:hover { color: var(--color-text); }
.footer-copy { font-size: 0.8rem; color: var(--color-text-muted); }

/* ===== Search Overlay ===== */
.search-overlay {
  position: fixed; inset: 0; z-index: 200;
  background: rgba(15, 23, 42, 0.5);
  backdrop-filter: blur(6px);
  display: flex; align-items: flex-start; justify-content: center;
  padding: 8vh 1rem 10vh;
  opacity: 0; pointer-events: none;
  transition: opacity 0.2s;
}
.search-overlay.open { opacity: 1; pointer-events: all; }
.search-box {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border);
  width: 100%; max-width: 600px;
  max-height: 78vh;
  box-shadow: var(--shadow-lg);
  display: flex; flex-direction: column;
  overflow: hidden;
}
.search-input-wrap { display: flex; align-items: center; padding: 1rem 1.5rem; border-bottom: 1px solid var(--color-border); gap: 0.75rem; flex-shrink: 0; }
.search-input-wrap svg { color: var(--color-text-muted); flex-shrink: 0; }
#search-input { border: none; outline: none; font-size: 1.05rem; flex: 1; font-family: var(--font-body); padding: 0.25rem 0; color: var(--color-text); background: transparent; }
.search-close { background: none; border: none; cursor: pointer; color: var(--color-text-muted); font-size: 1.1rem; padding: 0.25rem; border-radius: var(--radius-sm); }
.search-close:hover { background: var(--color-bg); }
.search-results { overflow-y: auto; max-height: calc(78vh - 5rem); min-height: 0; }
.search-result-item { padding: 1rem 1.5rem; border-bottom: 1px solid var(--color-border); cursor: pointer; transition: background var(--transition); }
.search-result-item:hover { background: var(--color-bg); }
.search-result-item h4 { font-size: 0.95rem; margin-bottom: 0.25rem; color: var(--color-text); }
.search-result-item p { font-size: 0.8rem; color: var(--color-text-muted); margin: 0 0 0.2rem; }
.search-snippet { font-size: 0.78rem; color: var(--color-text-muted); line-height: 1.5; }
.search-result-item mark { background: #fef08a; color: inherit; border-radius: 2px; padding: 0 1px; }
.search-empty { padding: 2rem; text-align: center; color: var(--color-text-muted); }

/* ===== Breadcrumb ===== */
.breadcrumb {
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  padding: 0.75rem 1.5rem;
}
.breadcrumb-inner { max-width: var(--content-max); margin: 0 auto; display: flex; align-items: center; gap: 0.5rem; font-size: 0.85rem; color: var(--color-text-muted); flex-wrap: nowrap; min-width: 0; overflow: hidden; }
.breadcrumb a { color: var(--color-text-muted); white-space: nowrap; flex-shrink: 0; }
.breadcrumb a:hover { color: var(--color-primary); }
.breadcrumb-sep { color: #cbd5e1; flex-shrink: 0; }
.breadcrumb-current { color: var(--color-text); font-weight: 500; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; min-width: 0; }

/* ===== Guide Layout ===== */
.guide-layout {
  max-width: var(--content-max);
  margin: 0 auto;
  padding: 2.5rem 1.5rem;
  display: grid;
  grid-template-columns: var(--sidebar-w) 1fr;
  gap: 3rem;
  align-items: start;
}
.guide-content { min-width: 0; overflow-wrap: break-word; word-break: break-word; }
.guide-content h2 {
  margin-top: 2.5rem;
  margin-bottom: 1rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--color-border);
}
.guide-content h3 { margin-top: 1.75rem; margin-bottom: 0.75rem; }
.guide-sidebar { position: sticky; top: 84px; }

/* ===== Guide Meta ===== */
.guide-meta {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin: 1rem 0 1.75rem;
}
.meta-badge {
  display: inline-flex; align-items: center; gap: 0.3rem;
  padding: 0.3rem 0.8rem;
  border-radius: var(--radius-pill);
  font-family: var(--font-body);
  font-size: 0.75rem;
  font-weight: 600;
}
.badge-difficulty-beginner { background: #dcfce7; color: #166534; }
.badge-difficulty-intermediate { background: #fef9c3; color: #854d0e; }
.badge-difficulty-advanced { background: #fee2e2; color: #991b1b; }
.badge-time { background: #f1f5f9; color: #475569; }
.badge-category { color: #fff; }
a.badge-category { text-decoration: none; cursor: pointer; transition: opacity var(--transition); }
a.badge-category:hover { opacity: 0.82; }
a.badge-difficulty-beginner, a.badge-difficulty-intermediate, a.badge-difficulty-advanced { text-decoration: none; cursor: pointer; transition: filter var(--transition), transform var(--transition); }
a.badge-difficulty-beginner:hover, a.badge-difficulty-intermediate:hover, a.badge-difficulty-advanced:hover { filter: brightness(0.9); transform: translateY(-1px); }
.badge-category.active { background: var(--color-primary); color: #fff; }
.badge-systemdesign { background: var(--cat-systemdesign); }

/* ===== Sidebar Widget ===== */
.sidebar-info-link {
  color: inherit;
  text-decoration: none;
  font-weight: 600;
  transition: color var(--transition);
}
.sidebar-info-link:hover { color: var(--color-primary); }
.sidebar-widget {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  margin-bottom: 1.25rem;
  box-shadow: var(--shadow-sm);
}
.sidebar-widget h4 { font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.08em; color: var(--color-text-muted); margin-bottom: 1rem; }
.toc-list { list-style: none; padding: 0; display: flex; flex-direction: column; gap: 0.2rem; }
.toc-list a {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  display: block;
  padding: 0.25rem 0.6rem;
  border-radius: var(--radius-sm);
  border-left: 2px solid transparent;
  transition: color var(--transition), background var(--transition), border-color var(--transition);
}
.toc-list a:hover, .toc-list a.active { color: var(--color-primary); background: var(--color-primary-light); border-left-color: var(--color-primary); text-decoration: none; }
.sidebar-chapter { margin-bottom: 0.75rem; }
.sidebar-chapter:last-child { margin-bottom: 0; }
.sidebar-chapter-label { display: block; font-size: 0.7rem; font-weight: 700; letter-spacing: 0.06em; text-transform: uppercase; color: var(--color-text-muted); margin-bottom: 0.25rem; opacity: 0.7; }
.sidebar-guides { list-style: none; padding: 0; display: flex; flex-direction: column; gap: 0.35rem; }
.sidebar-guides a { font-size: 0.875rem; color: var(--color-text-muted); padding: 0.3rem 0; display: block; }
.sidebar-guides a:hover { color: var(--color-primary); }
.sidebar-guides a.current { color: var(--color-primary); font-weight: 600; }

/* ===== Guide Nav (prev/next) ===== */
.guide-nav {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
  margin-top: 4rem;
  border-top: 1px solid var(--color-border);
  padding-top: 2rem;
}

.guide-nav-prev, .guide-nav-next {
  display: flex;
  flex-direction: column;
}

.guide-nav-next {
  align-items: flex-end;
  text-align: right;
}

.guide-nav-next .guide-nav-card {
  align-items: flex-end;
}

.guide-nav-card {
  display: flex;
  flex-direction: column;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  text-decoration: none;
  color: inherit;
  transition: all var(--transition);
  box-shadow: var(--shadow-sm);
  width: 100%;
}

.guide-nav-card:hover {
  box-shadow: var(--shadow-md);
  border-color: var(--color-primary);
  transform: translateY(-2px);
  text-decoration: none;
}

.guide-nav-label {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.5rem;
}

.guide-nav-title {
  font-weight: 700;
  color: var(--color-primary);
  margin-bottom: 0.25rem;
  display: block;
}

.guide-nav-sub {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  line-height: 1.4;
  display: block;
}

/* ===== 404 ===== */
.error-page { min-height: 70vh; display: flex; align-items: center; justify-content: center; text-align: center; padding: 2rem; }
.error-code { font-family: var(--font-display); font-size: 8rem; font-weight: 800; color: #d1d5db; line-height: 1; }
.error-title { font-size: 1.5rem; margin-bottom: 0.75rem; }

/* ===== Responsive ===== */
@media (max-width: 900px) {
  .guide-layout { grid-template-columns: 1fr; }
  .guide-sidebar { display: none; }
}

@media (max-width: 768px) {
  .nav-chapters { display: none; }
  .nav-progress-label { display: none; }
  .search-label { display: none; }
  .hero { padding: 3rem 1.5rem; }
  .hero-inner { grid-template-columns: 1fr; gap: 2rem; }
  .hero-right { display: flex; justify-content: center; }
  .guide-nav { grid-template-columns: 1fr; }
  .guide-nav-next, .guide-nav-next .guide-nav-card { align-items: flex-start; text-align: left; }
  .guides-grid { grid-template-columns: 1fr; }
  .search-box { width: 100%; max-width: 100%; }
}

@media (max-width: 600px) {
  #nav-cta { display: none; }
}

@media (max-width: 480px) {
  .section { padding: 2.5rem 1rem; }
  .hero { padding: 2rem 1rem 2.5rem; }
  .breadcrumb { padding: 0.5rem 1rem; }
  .guide-layout { padding: 1.5rem 1rem; }
  .categories-grid { grid-template-columns: 1fr; }
  .stats-bar { gap: 1.25rem; flex-wrap: wrap; justify-content: center; }
  .guide-nav-card { padding: 0.75rem 1rem; }
  .nav-inner { padding: 0 1rem; gap: 0.5rem; }
  .nav-progress { display: none; }
  h1 { font-size: clamp(1.75rem, 7vw, 2.4rem); }
  h2 { font-size: clamp(1.2rem, 5vw, 1.6rem); }
  .hero h1 { font-size: clamp(1.75rem, 8vw, 2.4rem); }
  .guide-content h1 { font-size: clamp(1.5rem, 7vw, 2rem); }
}

@media (max-width: 375px) {
  .nav-inner { padding: 0 0.75rem; gap: 0.35rem; }
  .nav-logo { font-size: 1.05rem; }
  .btn-primary { padding: 0.4rem 0.85rem; font-size: 0.8rem; }
  .search-btn { padding: 0.35rem 0.6rem; }
  .section { padding: 2rem 0.75rem; }
  .hero { padding: 1.75rem 0.75rem 2rem; }
  .guide-layout { padding: 1.25rem 0.75rem; }
}

/* ===== Dark Mode ===== */
:root { color-scheme: light; }

[data-theme="dark"] {
  color-scheme: dark;
  --color-bg: #0f172a;
  --color-surface: #1e293b;
  --color-border: #334155;
  --color-border-strong: #475569;
  --color-text: #f1f5f9;
  --color-text-muted: #94a3b8;
  --color-accent: #818cf8;
  --color-primary: #818cf8;
  --color-primary-light: rgba(129, 140, 248, 0.15);
  --shadow-sm: 0 1px 4px rgba(0, 0, 0, 0.35);
  --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.45);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.6);
}

body { transition: background-color 0.25s ease, color 0.25s ease; }

/* Theme toggle button */
.theme-toggle {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  color: var(--color-text-muted);
  width: 2.1rem; height: 2.1rem;
  display: flex; align-items: center; justify-content: center;
  cursor: pointer;
  flex-shrink: 0;
  transition: border-color var(--transition), color var(--transition), background var(--transition), transform var(--transition);
}
.theme-toggle:hover { border-color: var(--color-primary); color: var(--color-primary); transform: rotate(12deg); }
.theme-toggle .icon-sun { display: none; }
.theme-toggle .icon-moon { display: block; }
[data-theme="dark"] .theme-toggle .icon-sun { display: block; }
[data-theme="dark"] .theme-toggle .icon-moon { display: none; }

/* Hard-coded light color overrides */
[data-theme="dark"] code { background: #334155; color: #e2e8f0; }
[data-theme="dark"] pre code { background: none; color: #e2e8f0; }

[data-theme="dark"] .site-header {
  background: rgba(15, 23, 42, 0.78);
  border-bottom-color: rgba(51, 65, 85, 0.7);
}

[data-theme="dark"] #nav-cta {
  background: linear-gradient(135deg, rgba(129,140,248,0.18) 0%, rgba(167,139,250,0.12) 100%);
  border-color: rgba(167, 139, 250, 0.3);
  color: #a5b4fc;
}
[data-theme="dark"] #nav-cta:hover {
  background: linear-gradient(135deg, rgba(129,140,248,0.28) 0%, rgba(167,139,250,0.22) 100%);
  border-color: rgba(167, 139, 250, 0.55);
  color: #c7d2fe;
}

[data-theme="dark"] .btn-primary:hover { background: #6366f1; }

[data-theme="dark"] .badge-difficulty-beginner { background: rgba(34, 197, 94, 0.15); color: #4ade80; }
[data-theme="dark"] .badge-difficulty-intermediate { background: rgba(245, 158, 11, 0.15); color: #fbbf24; }
[data-theme="dark"] .badge-difficulty-advanced { background: rgba(239, 68, 68, 0.15); color: #f87171; }
[data-theme="dark"] .badge-time { background: #334155; color: #94a3b8; }

[data-theme="dark"] .search-result-item mark { background: rgba(253, 224, 71, 0.25); color: #fde047; }

[data-theme="dark"] .error-code { color: #334155; }
[data-theme="dark"] .breadcrumb-sep { color: #475569; }

/* ===== Reading progress bar ===== */
#reading-progress {
  position: fixed; top: 0; left: 0; height: 3px;
  background: var(--color-primary);
  transition: width 0.1s linear;
  z-index: 300;
  border-radius: 0 var(--radius-pill) var(--radius-pill) 0;
}

/* ===== Applause ===== */
@keyframes toast-glow {
  0%, 100% { box-shadow: 0 8px 40px rgba(79,70,229,0.35), 0 0 0 1px rgba(255,255,255,0.15), inset 0 1px 0 rgba(255,255,255,0.35); }
  50%       { box-shadow: 0 8px 56px rgba(124,58,237,0.55), 0 0 0 2px rgba(168,85,247,0.35), inset 0 1px 0 rgba(255,255,255,0.4); }
}
@keyframes toast-in {
  0%   { opacity: 0; transform: translateX(-50%) translateY(24px) scale(0.88); }
  60%  { transform: translateX(-50%) translateY(-4px) scale(1.03); }
  100% { opacity: 1; transform: translateX(-50%) translateY(0) scale(1); }
}
.applause-toast {
  position: fixed; bottom: 5rem; left: 50%; transform: translateX(-50%) translateY(20px);
  color: #fff;
  padding: 0.75rem 1.9rem;
  font-size: 0.92rem;
  font-weight: 700;
  letter-spacing: 0.01em;
  border-radius: var(--radius-pill);
  border: 1px solid rgba(168, 85, 247, 0.4);
  background: linear-gradient(135deg, rgba(79,70,229,0.72) 0%, rgba(124,58,237,0.68) 55%, rgba(168,85,247,0.6) 100%);
  backdrop-filter: blur(24px) saturate(220%) brightness(1.1);
  -webkit-backdrop-filter: blur(24px) saturate(220%) brightness(1.1);
  box-shadow: 0 8px 40px rgba(79,70,229,0.35), 0 0 0 1px rgba(255,255,255,0.15), inset 0 1px 0 rgba(255,255,255,0.35);
  z-index: 400; opacity: 0;
  transition: opacity 0.25s, transform 0.25s;
}
.applause-toast.show {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
  animation: toast-in 0.45s cubic-bezier(0.34,1.56,0.64,1) both, toast-glow 2.2s ease-in-out 0.45s infinite;
}
.applause-toast.hide { opacity: 0; transform: translateX(-50%) translateY(8px) scale(0.95); }
.applause-particle {
  position: fixed; bottom: 4rem; font-size: 1.5rem; z-index: 400; pointer-events: none;
  animation: particle-float var(--duration, 2s) ease-out forwards;
}
@keyframes particle-float {
  0%   { transform: translateY(0) translateX(0) scale(1); opacity: 1; }
  30%  { opacity: 1; }
  100% { transform: translateY(-200px) translateX(var(--drift, 0px)) scale(0.6); opacity: 0; }
}