/* ===== Design System ===== */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800&family=JetBrains+Mono:wght@400;500&display=swap');

:root {
  /* Colors – Dark theme (default) */
  --bg: #0a0a13;
  --bg2: #111120;
  --surface: rgba(255,255,255,0.04);
  --surface-hover: rgba(255,255,255,0.08);
  --border: rgba(255,255,255,0.08);
  --border-hover: rgba(255,255,255,0.18);
  --text: #e8e8f0;
  --text-muted: #7a7a99;
  --text-faint: #3a3a55;
  --accent: #6366f1;
  --accent2: #8b5cf6;
  --accent3: #06b6d4;
  --accent-glow: rgba(99,102,241,0.25);

  /* Category palette */
  --cat-rust: #f97316;
  --cat-algo: #22c55e;
  --cat-frontend: #06b6d4;
  --cat-backend: #a855f7;
  --cat-default: #6366f1;
  --cat-color: var(--cat-default);

  /* Spacing & shape */
  --radius: 16px;
  --radius-sm: 8px;
  --radius-pill: 999px;
  --transition: 0.28s cubic-bezier(0.4,0,0.2,1);
  --shadow: 0 4px 24px rgba(0,0,0,0.4);
  --shadow-lg: 0 12px 48px rgba(0,0,0,0.5);
}

[data-theme="light"] {
  --bg: #f0f0f8;
  --bg2: #e8e8f5;
  --surface: rgba(255,255,255,0.7);
  --surface-hover: rgba(255,255,255,0.9);
  --border: rgba(0,0,0,0.07);
  --border-hover: rgba(0,0,0,0.14);
  --text: #1a1a2e;
  --text-muted: #5a5a78;
  --text-faint: #c8c8e0;
  --accent-glow: rgba(99,102,241,0.15);
  --shadow: 0 4px 24px rgba(0,0,0,0.08);
  --shadow-lg: 0 12px 48px rgba(0,0,0,0.12);
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  font-family: 'Inter', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
  transition: background var(--transition), color var(--transition);
}

/* ===== Glass util ===== */
.glass {
  background: var(--surface);
  backdrop-filter: blur(20px) saturate(180%);
  -webkit-backdrop-filter: blur(20px) saturate(180%);
  border: 1px solid var(--border);
}

/* ===== Gradient text ===== */
.grad {
  background: linear-gradient(135deg, var(--accent), var(--accent2), var(--accent3));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero {
  position: sticky;
  top: 0;
  z-index: 1;
  min-height: 85vh; /* Occupy most of the screen */
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: 40px 24px;
  text-align: center;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  inset: -40%;
  background:
    radial-gradient(ellipse 60% 50% at 30% 40%, rgba(99,102,241,0.18) 0%, transparent 70%),
    radial-gradient(ellipse 50% 40% at 70% 60%, rgba(139,92,246,0.14) 0%, transparent 65%),
    radial-gradient(ellipse 40% 30% at 50% 20%, rgba(6,182,212,0.10) 0%, transparent 60%);
  pointer-events: none;
  animation: orb 12s ease-in-out infinite alternate;
}

@keyframes orb {
  from { transform: scale(1) rotate(0deg); }
  to   { transform: scale(1.08) rotate(3deg); }
}

.hero-tag {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent3);
  margin-bottom: 20px;
  padding: 4px 14px;
  border: 1px solid rgba(6,182,212,0.3);
  border-radius: var(--radius-pill);
  background: rgba(6,182,212,0.08);
}

.hero h1 {
  font-size: clamp(2.4rem, 6vw, 4.2rem);
  font-weight: 800;
  line-height: 1.1;
  letter-spacing: -0.03em;
  margin-bottom: 20px;
  min-height: 1.15em;
}

.hero-sub {
  font-size: 1.1rem;
  color: var(--text-muted);
  max-width: 520px;
  margin: 0 auto 32px;
  line-height: 1.7;
}

.hero-stats {
  display: flex;
  justify-content: center;
  gap: 40px;
  flex-wrap: wrap;
}

.stat {
  text-align: center;
}
.stat-num {
  font-size: 1.9rem;
  font-weight: 700;
  background: linear-gradient(135deg, var(--accent), var(--accent2));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  line-height: 1;
}
.stat-label {
  font-size: 0.78rem;
  color: var(--text-muted);
  margin-top: 4px;
  letter-spacing: 0.06em;
}

.toolbar {
  position: sticky;
  top: 0;
  z-index: 50;
  padding: 12px 24px;
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
  border-bottom: 1px solid var(--border);
  border-top: 1px solid var(--border);
  background: rgba(10,10,19,0.85);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
}

[data-theme="light"] .toolbar {
  background: rgba(240,240,248,0.85);
}

.search-wrap {
  flex: 1;
  min-width: 200px;
  position: relative;
}

.search-wrap svg {
  position: absolute;
  left: 12px;
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-muted);
  pointer-events: none;
}

#searchInput {
  width: 100%;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-pill);
  padding: 9px 16px 9px 40px;
  color: var(--text);
  font-size: 0.9rem;
  font-family: inherit;
  outline: none;
  transition: border-color var(--transition), box-shadow var(--transition);
}

#searchInput::placeholder { color: var(--text-muted); }
#searchInput:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

.categories {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  align-items: center;
}

.cat-chip {
  padding: 6px 14px;
  border-radius: var(--radius-pill);
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text-muted);
  font-size: 0.8rem;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition);
  white-space: nowrap;
}
.cat-chip:hover {
  border-color: var(--accent);
  color: var(--text);
  background: var(--accent-glow);
}
.cat-chip.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
  box-shadow: 0 0 12px var(--accent-glow);
}

.theme-btn {
  width: 38px;
  height: 38px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-size: 1.1rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition);
  flex-shrink: 0;
}
.theme-btn:hover { border-color: var(--accent); background: var(--accent-glow); }

/* ===== Main grid ===== */
.main {
  position: relative;
  z-index: 10;
  background: var(--bg); /* Opaque background hides the sticky hero behind it */
  max-width: 100%; /* Spans full width for covering */
  margin: 0;
  padding: 60px 0 120px;
  box-shadow: 0 -20px 40px rgba(0,0,0,0.3); /* Premium Apple-like shadow when covering */
}

/* Container for constraining width */
.main-inner {
  max-width: 1280px;
  margin: 0 auto;
  padding: 0 24px;
}

.section-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 28px;
}

.section-title {
  font-size: 1.3rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.result-count {
  font-size: 0.82rem;
  color: var(--text-muted);
}

.posts-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 24px;
}

/* ===== Post card ===== */
.post-card {
  position: relative;
  border-radius: var(--radius);
  background: var(--surface);
  border: 1px solid var(--border);
  overflow: hidden;
  cursor: pointer;
  transition: transform 0.8s cubic-bezier(0.16, 1, 0.3, 1), box-shadow var(--transition), border-color var(--transition), opacity 0.8s cubic-bezier(0.16, 1, 0.3, 1);
  text-decoration: none;
  color: var(--text);
  display: flex;
  flex-direction: column;
  opacity: 0;
  transform: translateY(80px); /* Larger starting offset for more drama */
}

.post-card.show {
  opacity: 1;
  transform: translateY(0);
}

.post-card.show:hover {
  transform: translateY(-8px);
  box-shadow: var(--shadow-lg), 0 0 0 1px var(--border-hover);
  border-color: var(--border-hover);
}

.card-banner {
  height: 6px;
  width: 100%;
}

.card-body {
  padding: 24px;
  flex: 1;
  display: flex;
  flex-direction: column;
}

.card-meta {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 14px;
}

.category-badge {
  font-size: 0.72rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  padding: 3px 10px;
  border-radius: var(--radius-pill);
  color: #fff;
  background: var(--cat-color, var(--cat-default));
}

.read-time {
  font-size: 0.78rem;
  color: var(--text-muted);
  margin-left: auto;
}

.card-title {
  font-size: 1.08rem;
  font-weight: 700;
  line-height: 1.4;
  margin-bottom: 10px;
  letter-spacing: -0.01em;
}

.card-desc {
  font-size: 0.87rem;
  color: var(--text-muted);
  line-height: 1.65;
  flex: 1;
}

.card-footer {
  padding: 14px 24px;
  border-top: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.card-date {
  font-size: 0.78rem;
  color: var(--text-faint);
  font-variant-numeric: tabular-nums;
}

.card-tags {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
}

.tag {
  font-size: 0.7rem;
  padding: 2px 8px;
  border-radius: var(--radius-pill);
  background: var(--surface-hover);
  color: var(--text-muted);
  border: 1px solid var(--border);
}

/* ===== Empty state ===== */
.empty-state {
  text-align: center;
  padding: 80px 24px;
  color: var(--text-muted);
  grid-column: 1 / -1;
}
.empty-state h3 { font-size: 1.2rem; margin-bottom: 8px; color: var(--text-faint); }

/* ===== Buttons ===== */
.btn-primary {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 22px;
  border-radius: var(--radius-pill);
  background: linear-gradient(135deg, var(--accent), var(--accent2));
  color: #fff;
  font-weight: 600;
  font-size: 0.9rem;
  text-decoration: none;
  transition: opacity var(--transition), transform var(--transition), box-shadow var(--transition);
  border: none;
  cursor: pointer;
}
.btn-primary:hover {
  opacity: 0.88;
  transform: translateY(-1px);
  box-shadow: 0 8px 24px var(--accent-glow);
}

/* ===== Post Page ===== */
.post-body {
  min-height: 100vh;
}

#reading-progress {
  position: fixed;
  top: 0;
  left: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--accent), var(--accent2), var(--accent3));
  width: 0%;
  z-index: 200;
  transition: width 0.08s linear;
}

.post-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 32px;
  gap: 16px;
  border-bottom: 1px solid var(--border);
  background: rgba(10,10,19,0.88);
  backdrop-filter: blur(16px);
}

[data-theme="light"] .post-nav {
  background: rgba(240,240,248,0.88);
}

.back-btn {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
  transition: color var(--transition);
}
.back-btn:hover { color: var(--accent); }

.post-nav-meta {
  display: flex;
  align-items: center;
  gap: 14px;
}

/* ===== Post layout ===== */
.post-layout {
  display: grid;
  grid-template-columns: 240px minmax(0, 1fr) 240px;
  max-width: 1400px;
  margin: 0 auto;
  padding: 40px 24px 80px;
  gap: 32px;
  align-items: start;
}

@media (max-width: 1100px) {
  .post-layout { grid-template-columns: 240px minmax(0, 1fr); }
  .toc-sidebar { display: none; }
}

@media (max-width: 860px) {
  .post-layout { grid-template-columns: 1fr; }
  .tree-sidebar { display: none; }
}

/* ===== Tree Sidebar ===== */
.tree-sidebar {
  position: sticky;
  top: 80px;
}

.tree-sidebar .toc-inner {
  max-height: calc(100vh - 100px);
  overflow-y: auto;
}
.tree-sidebar .toc-inner::-webkit-scrollbar { width: 4px; }
.tree-sidebar .toc-inner::-webkit-scrollbar-track { background: transparent; }
.tree-sidebar .toc-inner::-webkit-scrollbar-thumb { background: var(--border); border-radius: 2px; }

summary.tree-cat {
  cursor: pointer;
  list-style: none; /* remove default arrow */
  user-select: none;
  font-size: 0.8rem;
  font-weight: 800; /* Much bolder */
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text);
  margin: 0 0 6px 0;
  padding: 8px 10px;
  position: relative;
  border-radius: var(--radius-sm);
  background: var(--surface); /* distinctive background */
  border: 1px solid var(--border);
  transition: all var(--transition);
  display: flex;
  align-items: center;
  justify-content: space-between;
}
summary.tree-cat::-webkit-details-marker { display: none; }
summary.tree-cat::after { /* Use after to place the arrow on the right */
  content: '▼';
  font-size: 0.65rem;
  color: var(--text-faint);
  transition: transform var(--transition);
}
details:not([open]) summary.tree-cat::after {
  transform: rotate(-90deg);
}
summary.tree-cat:hover {
  background: var(--surface-hover);
  border-color: var(--border-hover);
}

.tree-group { margin-bottom: 12px; }
.tree-group:first-child summary.tree-cat { margin-top: 0; }
.tree-items { padding-left: 0; margin-bottom: 8px; }

.tree-item {
  display: block;
  padding: 6px 10px;
  font-size: 0.85rem;
  color: var(--text-muted);
  text-decoration: none;
  border-radius: var(--radius-sm);
  transition: all var(--transition);
  line-height: 1.4;
  margin-bottom: 2px;
}
.tree-item:hover {
  background: var(--surface-hover);
  color: var(--text);
}
.tree-item.active {
  background: var(--accent-glow);
  color: var(--accent);
  font-weight: 500;
}


.toc-sidebar {
  position: sticky;
  top: 80px;
}

.toc-inner {
  border-radius: var(--radius);
  padding: 20px;
}

.toc-title {
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: 14px;
}

#toc-nav a {
  display: block;
  padding: 5px 10px;
  font-size: 0.83rem;
  color: var(--text-muted);
  text-decoration: none;
  border-left: 2px solid var(--border);
  margin-bottom: 2px;
  border-radius: 0 4px 4px 0;
  transition: all var(--transition);
  line-height: 1.4;
}

#toc-nav a:hover,
#toc-nav a.active {
  color: var(--accent);
  border-left-color: var(--accent);
  background: var(--accent-glow);
}

#toc-nav .toc-h3 {
  padding-left: 22px;
  font-size: 0.78rem;
}

/* ===== Post article ===== */
.post-article {
  min-width: 0;
}

.post-header {
  margin-bottom: 48px;
  padding-bottom: 32px;
  border-bottom: 1px solid var(--border);
}

.post-tags {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 16px;
}

.post-title {
  font-size: clamp(1.8rem, 4vw, 2.8rem);
  font-weight: 800;
  line-height: 1.2;
  letter-spacing: -0.03em;
  margin-bottom: 16px;
}

.post-desc {
  font-size: 1.05rem;
  color: var(--text-muted);
  line-height: 1.7;
  margin-bottom: 20px;
}

.post-info {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 0.83rem;
  color: var(--text-faint);
}

/* ===== Markdown body ===== */
.markdown-body {
  font-size: 1.02rem;
  line-height: 1.85;
  color: var(--text);
}

.markdown-body h1,
.markdown-body h2,
.markdown-body h3,
.markdown-body h4 {
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.3;
  margin: 2.2em 0 0.8em;
  color: var(--text);
}
.markdown-body h1 { font-size: 2rem; }
.markdown-body h2 {
  font-size: 1.45rem;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
}
.markdown-body h3 { font-size: 1.18rem; }
.markdown-body h4 { font-size: 1rem; }

.markdown-body p { margin: 0 0 1.3em; }

.markdown-body a {
  color: var(--accent);
  text-decoration: none;
  border-bottom: 1px solid var(--accent-glow);
  transition: border-color var(--transition);
}
.markdown-body a:hover { border-color: var(--accent); }

.markdown-body strong { color: var(--text); font-weight: 600; }
.markdown-body em { color: var(--text-muted); }

.markdown-body blockquote {
  border-left: 3px solid var(--accent);
  margin: 1.8em 0;
  padding: 16px 24px;
  background: var(--accent-glow);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  color: var(--text-muted);
  font-style: italic;
}

.markdown-body ul,
.markdown-body ol {
  padding-left: 1.6em;
  margin: 0 0 1.3em;
}
.markdown-body li { margin: 0.35em 0; }

.markdown-body code {
  font-family: 'JetBrains Mono', 'Fira Code', monospace;
  font-size: 0.88em;
  background: rgba(99,102,241,0.12);
  padding: 2px 7px;
  border-radius: 5px;
  color: var(--accent3);
}

.markdown-body pre {
  background: #0d0d1e;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 22px 24px;
  overflow-x: auto;
  margin: 1.8em 0;
  font-size: 0.88rem;
  line-height: 1.65;
}

[data-theme="light"] .markdown-body pre {
  background: #1e1e3a;
}

.markdown-body pre code {
  background: none;
  padding: 0;
  color: #c9d1d9;
  font-size: inherit;
}

.markdown-body table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.8em 0;
  font-size: 0.92rem;
}
.markdown-body th {
  background: var(--surface-hover);
  padding: 10px 16px;
  font-weight: 600;
  text-align: left;
  border-bottom: 2px solid var(--border);
}
.markdown-body td {
  padding: 9px 16px;
  border-bottom: 1px solid var(--border);
}
.markdown-body tr:last-child td { border-bottom: none; }

.markdown-body hr {
  border: none;
  border-top: 1px solid var(--border);
  margin: 2.5em 0;
}

.markdown-body img {
  max-width: 100%;
  border-radius: var(--radius-sm);
}

/* ===== Post footer ===== */
.post-footer {
  margin-top: 60px;
  padding-top: 32px;
  border-top: 1px solid var(--border);
}

/* ===== Scrollbar ===== */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--accent); }

/* ===== Selection ===== */
::selection { background: var(--accent-glow); color: var(--text); }

/* ===== Responsive ===== */
@media (max-width: 600px) {
  .hero { padding: 64px 20px 48px; }
  .main { padding: 24px 16px 60px; }
  .toolbar { padding: 10px 16px; }
  .posts-grid { grid-template-columns: 1fr; }
  .hero-stats { gap: 24px; }
}