/* ============================================
   AI Evolution Website - Shared Styles v2
   From Transformer to Agent
   Consistent dark theme across all pages
   ============================================ */

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

:root {
  --bg-primary: #0a0e17;
  --bg-secondary: #111827;
  --bg-card: #1a2235;
  --bg-card-hover: #1f2a40;
  --text-primary: #e2e8f0;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --accent-blue: #3b82f6;
  --accent-purple: #8b5cf6;
  --accent-cyan: #06b6d4;
  --accent-green: #10b981;
  --accent-orange: #f59e0b;
  --accent-pink: #ec4899;
  --accent-red: #ef4444;
  --gradient-1: linear-gradient(135deg, #3b82f6, #8b5cf6);
  --gradient-2: linear-gradient(135deg, #06b6d4, #3b82f6);
  --gradient-3: linear-gradient(135deg, #8b5cf6, #ec4899);
  --border-color: #1e293b;
  --border-light: #334155;
  --code-bg: #0d1117;
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace;
  --shadow-sm: 0 1px 2px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.4);
  --shadow-lg: 0 8px 30px rgba(0,0,0,0.5);
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --content-width: 880px;
}

html { scroll-behavior: smooth; }
body {
  font-family: var(--font-sans);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.8;
  font-size: 16px;
  overflow-x: hidden;
  min-height: 100vh;
}

a { color: var(--accent-blue); text-decoration: none; transition: color 0.2s; }
a:hover { color: var(--accent-cyan); }

/* ============================================
   NAVIGATION - Consistent across all pages
   ============================================ */
.top-nav {
  position: fixed; top: 0; left: 0; right: 0; z-index: 1000;
  background: rgba(10, 14, 23, 0.92);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border-color);
  height: 60px;
}
.top-nav .nav-inner {
  max-width: 1200px; margin: 0 auto; padding: 0 1.5rem;
  height: 100%; display: flex; align-items: center; justify-content: space-between;
}
.nav-logo {
  font-size: 1rem; font-weight: 700; white-space: nowrap;
  background: var(--gradient-1); -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  background-clip: text;
}
.nav-links { display: flex; gap: 2px; align-items: center; }
.nav-links a {
  padding: 0.35rem 0.65rem; border-radius: var(--radius-sm);
  color: var(--text-muted); font-size: 0.82rem; font-weight: 500;
  transition: all 0.2s; white-space: nowrap;
}
.nav-links a:hover { color: var(--text-primary); background: rgba(59,130,246,0.08); }
.nav-links a.active { color: var(--accent-blue); background: rgba(59,130,246,0.12); }

/* ============================================
   PAGE HEADER - Consistent across content pages
   ============================================ */
.page-header {
  padding: 7rem 2rem 2.5rem; text-align: center;
  background: radial-gradient(ellipse at 50% 0%, rgba(59,130,246,0.1) 0%, transparent 55%), var(--bg-primary);
}
.page-header .chapter-num {
  display: inline-block; padding: 0.25rem 0.75rem; border-radius: 999px;
  background: rgba(59,130,246,0.1); border: 1px solid rgba(59,130,246,0.25);
  color: var(--accent-blue); font-size: 0.78rem; font-weight: 600; margin-bottom: 0.75rem;
  letter-spacing: 0.05em;
}
.page-header h1 {
  font-size: clamp(1.8rem, 4vw, 2.8rem); font-weight: 800; margin-bottom: 0.75rem;
  background: var(--gradient-1); -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  background-clip: text;
}
.page-header .subtitle {
  font-size: 1.05rem; color: var(--text-secondary); max-width: 650px; margin: 0 auto;
  line-height: 1.6;
}

/* ============================================
   HERO - Index page only
   ============================================ */
.hero {
  min-height: 100vh; display: flex; align-items: center; justify-content: center;
  text-align: center; padding: 5rem 2rem 3rem;
  background: radial-gradient(ellipse at 50% 0%, rgba(59,130,246,0.12) 0%, transparent 55%),
              radial-gradient(ellipse at 80% 50%, rgba(139,92,246,0.08) 0%, transparent 50%),
              var(--bg-primary);
}
.hero-content { max-width: 780px; }
.hero h1 {
  font-size: clamp(2.2rem, 5vw, 3.8rem); font-weight: 800; line-height: 1.15; margin-bottom: 1.25rem;
  background: linear-gradient(135deg, #e2e8f0 0%, #3b82f6 50%, #8b5cf6 100%);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  background-clip: text;
}
.hero p { font-size: 1.1rem; color: var(--text-secondary); max-width: 580px; margin: 0 auto 2rem; line-height: 1.7; }
.hero-badge {
  display: inline-block; padding: 0.35rem 0.9rem; border-radius: 999px;
  background: rgba(59,130,246,0.1); border: 1px solid rgba(59,130,246,0.25);
  color: var(--accent-blue); font-size: 0.82rem; font-weight: 500; margin-bottom: 1.25rem;
}

/* ============================================
   MAIN CONTENT
   ============================================ */
.content {
  max-width: var(--content-width); margin: 0 auto; padding: 2.5rem 2rem 5rem;
}
.content h2 {
  font-size: 1.6rem; font-weight: 700; margin: 3.5rem 0 1rem;
  padding-bottom: 0.5rem; border-bottom: 1px solid var(--border-color);
  color: var(--text-primary);
}
.content h2:first-child { margin-top: 0; }
.content h3 {
  font-size: 1.25rem; font-weight: 600; margin: 2.5rem 0 0.75rem;
  color: var(--accent-blue);
}
.content h4 {
  font-size: 1.05rem; font-weight: 600; margin: 1.8rem 0 0.5rem;
  color: var(--accent-purple);
}
.content p { margin-bottom: 1rem; color: var(--text-secondary); line-height: 1.8; }
.content ul, .content ol { margin: 0.5rem 0 1.5rem 1.5rem; color: var(--text-secondary); }
.content li { margin-bottom: 0.5rem; line-height: 1.7; }
.content li ul, .content li ol { margin-top: 0.3rem; margin-bottom: 0.3rem; }
.content strong { color: var(--text-primary); font-weight: 600; }
.content em { color: var(--accent-cyan); font-style: normal; }

/* ============================================
   CARDS GRID
   ============================================ */
.cards-grid {
  display: grid; gap: 1.25rem; margin: 2rem 0;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
}
.card {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: var(--radius-lg); padding: 1.5rem; transition: all 0.25s;
  text-decoration: none; color: inherit; display: block;
}
.card:hover {
  border-color: rgba(59,130,246,0.4); transform: translateY(-2px);
  box-shadow: 0 4px 20px rgba(59,130,246,0.1); background: var(--bg-card-hover);
}
.card-icon { font-size: 1.8rem; margin-bottom: 0.6rem; display: block; }
.card h3 { font-size: 1.05rem; font-weight: 600; margin-bottom: 0.4rem; color: var(--text-primary); }
.card p { font-size: 0.88rem; color: var(--text-secondary); margin: 0; line-height: 1.6; }
.card-tag {
  display: inline-block; padding: 0.15rem 0.55rem; border-radius: 999px;
  font-size: 0.72rem; font-weight: 600; margin-top: 0.7rem;
  letter-spacing: 0.03em;
}
.tag-blue { background: rgba(59,130,246,0.12); color: var(--accent-blue); }
.tag-purple { background: rgba(139,92,246,0.12); color: var(--accent-purple); }
.tag-cyan { background: rgba(6,182,212,0.12); color: var(--accent-cyan); }
.tag-green { background: rgba(16,185,129,0.12); color: var(--accent-green); }
.tag-orange { background: rgba(245,158,11,0.12); color: var(--accent-orange); }
.tag-pink { background: rgba(236,72,153,0.12); color: var(--accent-pink); }

/* ============================================
   INFO BOXES
   ============================================ */
.info-box {
  background: var(--bg-card); border-left: 3px solid var(--accent-blue);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  padding: 1.1rem 1.4rem; margin: 1.5rem 0;
}
.info-box.warn { border-left-color: var(--accent-orange); }
.info-box.success { border-left-color: var(--accent-green); }
.info-box.purple { border-left-color: var(--accent-purple); }
.info-box.tip { border-left-color: var(--accent-cyan); }
.info-box h4 { margin-top: 0; margin-bottom: 0.4rem; font-size: 0.95rem; color: var(--text-primary); }
.info-box p { margin-bottom: 0.4rem; font-size: 0.9rem; }
.info-box p:last-child { margin-bottom: 0; }
.info-box ul { margin: 0.3rem 0 0 1.2rem; font-size: 0.9rem; }
.info-box li { margin-bottom: 0.2rem; }

/* ============================================
   CODE BLOCKS
   ============================================ */
.code-block {
  background: var(--code-bg); border: 1px solid var(--border-color);
  border-radius: var(--radius-md); padding: 1.2rem 1.4rem; margin: 1.2rem 0;
  overflow-x: auto; font-family: var(--font-mono); font-size: 0.85rem;
  line-height: 1.65; color: #c9d1d9; white-space: pre;
}
.code-block .comment { color: #6e7681; }
.code-block .keyword { color: #ff7b72; }
.code-block .string { color: #a5d6ff; }
.code-block .function { color: #d2a8ff; }
.code-block .number { color: #79c0ff; }
.code-label {
  display: inline-block; background: rgba(59,130,246,0.1); color: var(--accent-blue);
  font-size: 0.75rem; font-weight: 600; padding: 0.15rem 0.5rem;
  border-radius: var(--radius-sm) var(--radius-sm) 0 0; margin-bottom: -1px;
  font-family: var(--font-mono);
}

/* ============================================
   MATH FORMULAS
   ============================================ */
.formula {
  background: var(--code-bg); border: 1px solid var(--border-color);
  border-radius: var(--radius-md); padding: 0.9rem 1.4rem; margin: 1rem 0;
  font-family: var(--font-mono); font-size: 0.9rem; text-align: center;
  color: var(--accent-cyan); overflow-x: auto; line-height: 1.8;
}
.formula-label {
  display: block; font-size: 0.75rem; color: var(--text-muted);
  margin-bottom: 0.3rem; font-family: var(--font-sans); text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* ============================================
   DIAGRAM CONTAINER
   ============================================ */
.diagram-container {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: var(--radius-lg); padding: 1.5rem; margin: 2rem 0;
  overflow-x: auto;
}
.diagram-title {
  font-size: 0.9rem; font-weight: 600; color: var(--text-primary);
  margin-bottom: 1.2rem; text-align: center;
}
.diagram-container svg { display: block; margin: 0 auto; max-width: 100%; height: auto; }

/* ============================================
   FLOW DIAGRAMS (CSS-based)
   ============================================ */
.flow-diagram { display: flex; flex-direction: column; align-items: center; gap: 0.4rem; margin: 1.5rem 0; }
.flow-row { display: flex; align-items: center; gap: 0.6rem; flex-wrap: wrap; justify-content: center; }
.flow-box {
  padding: 0.55rem 1.1rem; border-radius: var(--radius-sm);
  font-size: 0.85rem; font-weight: 600; text-align: center;
  min-width: 100px; border: 1px solid transparent;
}
.flow-box.blue { background: rgba(59,130,246,0.12); color: var(--accent-blue); border-color: rgba(59,130,246,0.25); }
.flow-box.purple { background: rgba(139,92,246,0.12); color: var(--accent-purple); border-color: rgba(139,92,246,0.25); }
.flow-box.cyan { background: rgba(6,182,212,0.12); color: var(--accent-cyan); border-color: rgba(6,182,212,0.25); }
.flow-box.green { background: rgba(16,185,129,0.12); color: var(--accent-green); border-color: rgba(16,185,129,0.25); }
.flow-box.orange { background: rgba(245,158,11,0.12); color: var(--accent-orange); border-color: rgba(245,158,11,0.25); }
.flow-box.pink { background: rgba(236,72,153,0.12); color: var(--accent-pink); border-color: rgba(236,72,153,0.25); }
.flow-box.red { background: rgba(239,68,68,0.12); color: var(--accent-red); border-color: rgba(239,68,68,0.25); }
.flow-arrow { color: var(--text-muted); font-size: 1.1rem; }
.flow-arrow-down { color: var(--text-muted); font-size: 1.1rem; display: block; text-align: center; }

/* ============================================
   TABLES
   ============================================ */
.styled-table {
  width: 100%; border-collapse: collapse; margin: 1.5rem 0;
  background: var(--bg-card); border-radius: var(--radius-md); overflow: hidden;
  border: 1px solid var(--border-color); font-size: 0.88rem;
}
.styled-table th {
  background: rgba(59,130,246,0.08); color: var(--accent-blue);
  padding: 0.7rem 0.9rem; text-align: left; font-size: 0.8rem;
  font-weight: 600; text-transform: uppercase; letter-spacing: 0.04em;
  border-bottom: 1px solid var(--border-color);
}
.styled-table td {
  padding: 0.65rem 0.9rem; border-top: 1px solid var(--border-color);
  color: var(--text-secondary); vertical-align: top;
}
.styled-table tr:first-child td { border-top: none; }
.styled-table tr:hover td { background: rgba(59,130,246,0.03); }
.styled-table code {
  background: var(--code-bg); padding: 0.1rem 0.35rem; border-radius: 3px;
  font-size: 0.82rem; color: var(--accent-cyan); font-family: var(--font-mono);
}

/* ============================================
   TIMELINE
   ============================================ */
.timeline { position: relative; padding-left: 2rem; margin: 2rem 0; }
.timeline::before {
  content: ''; position: absolute; left: 7px; top: 4px; bottom: 4px;
  width: 2px; background: var(--border-light);
}
.timeline-item { position: relative; margin-bottom: 1.8rem; }
.timeline-item::before {
  content: ''; position: absolute; left: -1.72rem; top: 6px;
  width: 10px; height: 10px; border-radius: 50%; background: var(--accent-blue);
  border: 2px solid var(--bg-primary); box-shadow: 0 0 0 2px var(--accent-blue);
}
.timeline-item .year {
  font-size: 0.8rem; font-weight: 700; color: var(--accent-blue); margin-bottom: 0.15rem;
  font-family: var(--font-mono);
}
.timeline-item h4 { font-size: 1rem; margin: 0 0 0.25rem; color: var(--text-primary); }
.timeline-item p { font-size: 0.88rem; color: var(--text-secondary); margin: 0; line-height: 1.65; }

/* ============================================
   COMPARISON LAYOUT
   ============================================ */
.comparison {
  display: grid; grid-template-columns: 1fr 1fr; gap: 1.25rem; margin: 1.5rem 0;
}
.comparison > div {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: var(--radius-md); padding: 1.2rem;
}
.comparison > div h4 { margin-top: 0; }

/* ============================================
   BOTTOM NAVIGATION
   ============================================ */
.bottom-nav {
  display: flex; justify-content: space-between; align-items: stretch;
  padding: 2rem 0; margin-top: 3rem; border-top: 1px solid var(--border-color);
  gap: 1rem;
}
.bottom-nav a {
  display: flex; flex-direction: column; gap: 0.2rem; padding: 0.8rem 1.2rem;
  border-radius: var(--radius-md); background: var(--bg-card);
  border: 1px solid var(--border-color); color: var(--text-secondary);
  font-size: 0.88rem; transition: all 0.2s; text-decoration: none;
  min-width: 160px;
}
.bottom-nav a:hover { border-color: rgba(59,130,246,0.4); color: var(--text-primary); }
.bottom-nav a.next { text-align: right; margin-left: auto; }
.bottom-nav .label { font-size: 0.72rem; color: var(--text-muted); text-transform: uppercase; letter-spacing: 0.05em; }
.bottom-nav .title { font-weight: 600; color: var(--text-primary); font-size: 0.9rem; }

/* ============================================
   FOOTER
   ============================================ */
.site-footer {
  text-align: center; padding: 1.5rem 2rem;
  border-top: 1px solid var(--border-color);
  color: var(--text-muted); font-size: 0.8rem;
}

/* ============================================
   LAYER STACK DIAGRAM
   ============================================ */
.layer-stack { display: flex; flex-direction: column; gap: 3px; margin: 1.5rem auto; max-width: 480px; }
.layer {
  padding: 0.6rem 1rem; border-radius: var(--radius-sm);
  text-align: center; font-weight: 600; font-size: 0.85rem;
}

/* ============================================
   INTERVIEW TIP BOXES
   ============================================ */
.interview-tip {
  background: rgba(245,158,11,0.06); border: 1px solid rgba(245,158,11,0.2);
  border-radius: var(--radius-md); padding: 1rem 1.2rem; margin: 1.5rem 0;
  position: relative;
}
.interview-tip::before {
  content: 'INTERVIEW'; position: absolute; top: -0.5rem; left: 1rem;
  background: var(--bg-primary); padding: 0 0.4rem; font-size: 0.65rem;
  font-weight: 700; color: var(--accent-orange); letter-spacing: 0.1em;
  font-family: var(--font-mono);
}
.interview-tip p { font-size: 0.9rem; color: var(--accent-orange); margin: 0; }
.interview-tip ul { font-size: 0.88rem; margin: 0.3rem 0 0 1.2rem; color: var(--text-secondary); }
.interview-tip li { margin-bottom: 0.2rem; }

/* ============================================
   RESPONSIVE
   ============================================ */
@media (max-width: 768px) {
  .top-nav .nav-inner { padding: 0 0.75rem; }
  .nav-links { gap: 0; }
  .nav-links a { padding: 0.3rem 0.4rem; font-size: 0.72rem; }
  .content { padding: 1.5rem 1rem 3rem; }
  .content h2 { font-size: 1.35rem; }
  .content h3 { font-size: 1.1rem; }
  .flow-row { flex-direction: column; gap: 0.3rem; }
  .bottom-nav { flex-direction: column; }
  .bottom-nav a { min-width: unset; }
  .bottom-nav a.next { text-align: left; }
  .comparison { grid-template-columns: 1fr; }
  .page-header { padding: 5.5rem 1rem 2rem; }
  .styled-table { font-size: 0.8rem; }
  .styled-table th, .styled-table td { padding: 0.5rem 0.6rem; }
}