/* ============================================================
   Checkpointless Training Deep Research
   Premium dark-first design inspired by Linear/Vercel/Stripe
   ============================================================ */
*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }

:root {
  --accent: #22D3EE;
  --accent-light: #67E8F9;
  --accent-dim: rgba(34,211,238,0.15);
  --accent-gradient: linear-gradient(135deg, #06B6D4, #22D3EE, #67E8F9);
  --accent-gradient-text: linear-gradient(135deg, #22D3EE, #A78BFA);
  --sidebar-w: 260px;
}

/* --- Dark Theme (default) --- */
[data-theme="dark"] {
  --bg-body: #09090B;
  --bg-sidebar: #0C0C0F;
  --bg-card: #18181B;
  --bg-code: #111113;
  --bg-hover: rgba(255,255,255,0.04);
  --bg-inset: #0F0F12;
  --text-primary: #FAFAFA;
  --text-secondary: #A1A1AA;
  --text-muted: #52525B;
  --border: rgba(255,255,255,0.06);
  --border-strong: rgba(255,255,255,0.1);
  --shadow: rgba(0,0,0,0.5);
  --sidebar-active-bg: rgba(34,211,238,0.08);
  --callout-info-bg: rgba(34,211,238,0.06);
  --callout-info-border: #22D3EE;
  --callout-warn-bg: rgba(250,204,21,0.06);
  --callout-warn-border: #FACC15;
  --callout-danger-bg: rgba(239,68,68,0.06);
  --callout-danger-border: #F87171;
  --callout-success-bg: rgba(52,211,153,0.06);
  --callout-success-border: #34D399;
  --table-stripe: rgba(255,255,255,0.02);
  --glow: 0 0 80px rgba(34,211,238,0.08);
}

/* --- Light Theme --- */
[data-theme="light"] {
  --bg-body: #FAFAFA;
  --bg-sidebar: #FFFFFF;
  --bg-card: #FFFFFF;
  --bg-code: #F4F4F5;
  --bg-hover: rgba(0,0,0,0.03);
  --bg-inset: #F4F4F5;
  --text-primary: #18181B;
  --text-secondary: #52525B;
  --text-muted: #A1A1AA;
  --border: rgba(0,0,0,0.06);
  --border-strong: rgba(0,0,0,0.1);
  --shadow: rgba(0,0,0,0.05);
  --sidebar-active-bg: rgba(6,182,212,0.06);
  --callout-info-bg: rgba(6,182,212,0.05);
  --callout-info-border: #0891B2;
  --callout-warn-bg: rgba(234,179,8,0.05);
  --callout-warn-border: #CA8A04;
  --callout-danger-bg: rgba(220,38,38,0.05);
  --callout-danger-border: #DC2626;
  --callout-success-bg: rgba(22,163,74,0.05);
  --callout-success-border: #16A34A;
  --table-stripe: rgba(0,0,0,0.015);
  --glow: none;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Noto Sans KR', 'Inter', 'Segoe UI', sans-serif;
  background: var(--bg-body);
  color: var(--text-primary);
  line-height: 1.8;
  font-size: 15px;
  transition: background 0.3s ease, color 0.3s ease;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--accent); text-decoration: none; transition: opacity 0.15s; }
a:hover { opacity: 0.8; text-decoration: none; }

::selection { background: var(--accent-dim); }

/* --- Layout --- */
.doc-layout { display: flex; min-height: 100vh; }

/* --- Sidebar --- */
.sidebar {
  position: fixed; top: 0; left: 0;
  width: var(--sidebar-w); height: 100vh;
  background: var(--bg-sidebar);
  border-right: 1px solid var(--border);
  overflow-y: auto; z-index: 100;
  display: flex; flex-direction: column;
  transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  backdrop-filter: blur(12px);
}
.sidebar::-webkit-scrollbar { width: 4px; }
.sidebar::-webkit-scrollbar-thumb { background: var(--border-strong); border-radius: 4px; }

.sidebar-header {
  padding: 24px 20px 20px;
  border-bottom: 1px solid var(--border);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: -0.01em;
  background: var(--accent-gradient-text);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.sidebar-header .subtitle {
  font-size: 11px;
  -webkit-text-fill-color: var(--text-muted);
  font-weight: 400;
  margin-top: 4px;
  letter-spacing: 0;
}

.sidebar-nav { flex: 1; padding: 16px 0; overflow-y: auto; }
.sidebar-section { margin-bottom: 4px; }
.sidebar-section-title {
  padding: 8px 20px 4px;
  font-size: 10px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--text-muted);
}

.sidebar-link {
  display: flex; align-items: center; gap: 10px;
  padding: 8px 20px;
  font-size: 13px;
  color: var(--text-secondary);
  border-left: 2px solid transparent;
  transition: all 0.15s ease;
  letter-spacing: -0.01em;
}
.sidebar-link:hover {
  background: var(--bg-hover);
  color: var(--text-primary);
  text-decoration: none;
}
.sidebar-link.active {
  background: var(--sidebar-active-bg);
  color: var(--accent);
  border-left-color: var(--accent);
  font-weight: 600;
}

.sidebar-link .part-num {
  display: inline-flex; align-items: center; justify-content: center;
  width: 20px; height: 20px;
  border-radius: 6px;
  background: var(--accent-dim);
  color: var(--accent);
  font-size: 11px; font-weight: 700;
  flex-shrink: 0;
  border: 1px solid rgba(34,211,238,0.2);
}

.sidebar-footer {
  padding: 12px 20px;
  border-top: 1px solid var(--border);
}
.sidebar-footer button {
  width: 100%; padding: 8px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: transparent;
  color: var(--text-secondary);
  cursor: pointer;
  font-size: 12px;
  display: flex; align-items: center; justify-content: center; gap: 6px;
  transition: all 0.15s;
}
.sidebar-footer button:hover { background: var(--bg-hover); border-color: var(--border-strong); }
.sidebar-footer svg { width: 14px; height: 14px; fill: currentColor; stroke: currentColor; }

/* --- Main Content --- */
.doc-main {
  margin-left: var(--sidebar-w);
  flex: 1; min-width: 0;
  padding: 48px 64px;
  max-width: calc(100% - var(--sidebar-w));
}
.doc-content { max-width: 960px; margin: 0 auto; }

/* --- Hero Banner --- */
.hero-banner {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 48px;
  margin-bottom: 48px;
  position: relative;
  overflow: hidden;
  box-shadow: var(--glow);
}
.hero-banner::before {
  content: '';
  position: absolute;
  top: -50%; right: -20%;
  width: 400px; height: 400px;
  background: radial-gradient(circle, rgba(34,211,238,0.1) 0%, transparent 70%);
  pointer-events: none;
}
.hero-banner h1 {
  font-size: 32px; font-weight: 800;
  margin-bottom: 12px;
  letter-spacing: -0.02em;
  background: var(--accent-gradient-text);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.hero-banner p {
  color: var(--text-secondary);
  font-size: 15px;
  line-height: 1.6;
}
.hero-meta {
  display: flex; gap: 12px; margin-top: 20px;
  font-size: 12px; font-weight: 500;
  color: var(--text-muted);
}
.hero-meta span {
  background: var(--accent-dim);
  color: var(--accent);
  padding: 5px 14px;
  border-radius: 100px;
  border: 1px solid rgba(34,211,238,0.15);
}

/* --- Typography --- */
h1 {
  font-size: 32px; font-weight: 800;
  margin: 32px 0 16px;
  letter-spacing: -0.02em;
}
h2 {
  font-size: 22px; font-weight: 700;
  margin: 56px 0 16px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border);
  letter-spacing: -0.01em;
  color: var(--text-primary);
}
h3 {
  font-size: 17px; font-weight: 600;
  margin: 36px 0 12px;
  color: var(--accent);
  letter-spacing: -0.01em;
}
h4 { font-size: 15px; font-weight: 600; margin: 24px 0 8px; }
p { margin: 0 0 16px; }
.lead { font-size: 16px; color: var(--text-secondary); margin-bottom: 28px; line-height: 1.7; }

/* --- Reading Time --- */
.reading-time {
  display: inline-flex; align-items: center; gap: 6px;
  background: var(--accent-dim);
  padding: 5px 14px;
  border-radius: 100px;
  font-size: 12px;
  color: var(--accent);
  margin-bottom: 24px;
  border: 1px solid rgba(34,211,238,0.12);
}

/* --- Callouts --- */
.callout {
  padding: 16px 20px;
  border-radius: 12px;
  border-left: 3px solid;
  margin: 20px 0;
  font-size: 14px;
  line-height: 1.7;
}
.callout strong { display: block; margin-bottom: 6px; font-size: 13px; letter-spacing: 0.02em; text-transform: uppercase; }
.callout.info { background: var(--callout-info-bg); border-color: var(--callout-info-border); }
.callout.info strong { color: var(--callout-info-border); }
.callout.warning { background: var(--callout-warn-bg); border-color: var(--callout-warn-border); }
.callout.warning strong { color: var(--callout-warn-border); }
.callout.danger { background: var(--callout-danger-bg); border-color: var(--callout-danger-border); }
.callout.danger strong { color: var(--callout-danger-border); }
.callout.success { background: var(--callout-success-bg); border-color: var(--callout-success-border); }
.callout.success strong { color: var(--callout-success-border); }

/* --- Tables --- */
table {
  width: 100%; border-collapse: collapse;
  margin: 20px 0; font-size: 13px;
}
th, td {
  padding: 10px 16px;
  border: 1px solid var(--border);
  text-align: left;
}
th {
  background: var(--bg-card);
  font-weight: 600;
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  color: var(--text-muted);
}
td { color: var(--text-secondary); }
tr:nth-child(even) { background: var(--table-stripe); }

/* --- Code Blocks --- */
pre {
  background: var(--bg-code);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px;
  overflow-x: auto;
  margin: 20px 0;
  font-size: 13px;
  line-height: 1.65;
}
code {
  font-family: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', 'SF Mono', monospace;
  font-size: 0.88em;
}
:not(pre) > code {
  background: var(--accent-dim);
  color: var(--accent);
  padding: 2px 7px;
  border-radius: 6px;
  font-size: 0.85em;
}
.code-comment { color: #52525B; }
.code-keyword { color: #F472B6; }
.code-string { color: #34D399; }
.code-number { color: #67E8F9; }

/* --- Cards --- */
.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 24px;
  margin: 20px 0;
  transition: all 0.2s ease;
}
.card:hover { border-color: var(--border-strong); box-shadow: var(--glow); }
.card h4 { margin-top: 0; }

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
  margin: 20px 0;
}

/* --- Details/Collapsible --- */
details {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 12px;
  margin: 16px 0;
  overflow: hidden;
  transition: border-color 0.2s;
}
details:hover { border-color: var(--border-strong); }
details summary {
  padding: 14px 20px;
  cursor: pointer;
  font-weight: 600;
  font-size: 14px;
  list-style: none;
  display: flex; align-items: center; gap: 10px;
  color: var(--text-primary);
  transition: color 0.15s;
}
details summary::before {
  content: '▸';
  font-size: 12px;
  transition: transform 0.2s ease;
  color: var(--accent);
}
details[open] summary::before { transform: rotate(90deg); }
details summary::-webkit-details-marker { display: none; }
details > div, details > p { padding: 0 20px 20px; }
details[open] { border-color: var(--accent-dim); }

/* --- Formula --- */
.formula {
  background: var(--bg-inset);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px;
  margin: 16px 0;
  font-family: 'JetBrains Mono', 'Fira Code', monospace;
  font-size: 14px;
  text-align: center;
  overflow-x: auto;
  color: var(--accent-light);
}

/* --- Badges --- */
.badge {
  display: inline-block;
  padding: 3px 10px;
  border-radius: 100px;
  font-size: 10px;
  font-weight: 600;
  letter-spacing: 0.03em;
  text-transform: uppercase;
}
.badge-aws { background: rgba(255,153,0,0.15); color: #FB923C; border: 1px solid rgba(255,153,0,0.2); }
.badge-nvidia { background: rgba(118,185,0,0.15); color: #84CC16; border: 1px solid rgba(118,185,0,0.2); }
.badge-pytorch { background: rgba(238,76,44,0.15); color: #F87171; border: 1px solid rgba(238,76,44,0.2); }
.badge-google { background: rgba(66,133,244,0.15); color: #60A5FA; border: 1px solid rgba(66,133,244,0.2); }
.badge-paper { background: rgba(139,92,246,0.15); color: #A78BFA; border: 1px solid rgba(139,92,246,0.2); }

/* --- Navigation Footer --- */
.nav-footer {
  display: flex;
  justify-content: space-between;
  margin-top: 64px;
  padding-top: 32px;
  border-top: 1px solid var(--border);
}
.nav-footer a {
  display: flex; flex-direction: column; gap: 4px;
  padding: 16px 24px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 12px;
  font-size: 14px;
  transition: all 0.2s ease;
  max-width: 45%;
}
.nav-footer a:hover {
  border-color: var(--accent);
  box-shadow: var(--glow);
  text-decoration: none;
  opacity: 1;
}
.nav-label { font-size: 11px; color: var(--text-muted); text-transform: uppercase; letter-spacing: 0.05em; }

/* --- Mobile Toggle --- */
.sidebar-toggle {
  display: none;
  position: fixed; top: 16px; left: 16px;
  z-index: 200;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 10px;
  cursor: pointer;
  color: var(--text-primary);
  backdrop-filter: blur(8px);
}
.sidebar-overlay {
  display: none;
  position: fixed; inset: 0;
  background: rgba(0,0,0,0.6);
  backdrop-filter: blur(4px);
  z-index: 99;
}
.sidebar-overlay.open { display: block; }

/* --- Progress Bar --- */
.progress-bar {
  position: fixed; top: 0; left: 0;
  width: 0%; height: 2px;
  background: var(--accent-gradient);
  z-index: 1000;
  transition: width 0.1s;
  box-shadow: 0 0 12px rgba(34,211,238,0.4);
}

/* --- Comparison Flow --- */
.compare-flow {
  display: flex; align-items: center;
  gap: 12px; margin: 20px 0; flex-wrap: wrap;
}
.compare-flow .step-box {
  background: var(--bg-card);
  border: 1px solid var(--border);
  padding: 14px 18px;
  border-radius: 10px;
  font-size: 13px;
  text-align: center;
  min-width: 120px;
  transition: all 0.2s;
}
.compare-flow .step-box small { display: block; color: var(--text-muted); font-size: 11px; margin-top: 4px; }
.compare-flow .arrow { color: var(--accent); font-size: 18px; opacity: 0.6; }
.compare-flow .step-box.highlight {
  border-color: var(--accent);
  background: var(--accent-dim);
  box-shadow: var(--glow);
}

/* --- Responsive --- */
@media (max-width: 1024px) {
  .sidebar { transform: translateX(-100%); }
  .sidebar.open { transform: translateX(0); }
  .sidebar-toggle { display: block; }
  .doc-main { margin-left: 0; padding: 64px 24px 48px; max-width: 100%; }
}

/* --- Print --- */
@media print {
  .sidebar, .sidebar-toggle, .sidebar-overlay, .progress-bar, .nav-footer, .sidebar-footer { display: none !important; }
  .doc-main { margin-left: 0 !important; padding: 0 !important; max-width: 100% !important; }
  body { background: #fff !important; color: #000 !important; font-size: 12px !important; }
  h2 { page-break-before: always; border-color: #ccc !important; }
  pre { border: 1px solid #ddd !important; background: #f9f9f9 !important; }
  .callout { border: 1px solid #ddd !important; background: #f9f9f9 !important; }
  a { color: #000 !important; }
  .hero-banner h1 { -webkit-text-fill-color: #000 !important; background: none !important; }
  .formula { color: #000 !important; }
  code { color: #000 !important; background: #eee !important; }
}