/* ===== RESET & BASE ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: 'Inter', ui-sans-serif, system-ui, -apple-system, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  min-height: 100vh;
}
a { color: inherit; text-decoration: none; }

/* ===== CSS CUSTOM PROPERTIES ===== */
:root {
  --bg-primary: #0f172a;
  --bg-secondary: #1e1b4b;
  --bg-card: rgba(30, 27, 75, 0.35);
  --bg-card-hover: rgba(30, 27, 75, 0.55);
  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --text-emphasis: #e2e8f0;
  --cyan: #06b6d4;
  --cyan-light: #22d3ee;
  --violet: #8b5cf6;
  --violet-light: #a78bfa;
  --amber: #f59e0b;
  --amber-light: #fbbf24;
  --emerald: #10b981;
  --rose: #f43f5e;
  --border: rgba(148, 163, 184, 0.08);
  --border-hover: rgba(148, 163, 184, 0.18);
  --container-max: 1280px;
  --transition-fast: 0.2s ease;
  --transition-medium: 0.35s ease;
}

/* ===== BACKGROUNDS ===== */
.page-bg {
  position: fixed; inset: 0; z-index: 0; pointer-events: none;
  background: linear-gradient(160deg, #0f172a 0%, #1e1b4b 40%, #0f172a 100%);
}
.grid-bg {
  position: fixed; inset: 0; z-index: 0; pointer-events: none;
  background-image:
    linear-gradient(rgba(99,102,241,0.04) 1px, transparent 1px),
    linear-gradient(90deg, rgba(99,102,241,0.04) 1px, transparent 1px);
  background-size: 50px 50px;
}

/* ===== LAYOUT ===== */
.container { max-width: var(--container-max); margin: 0 auto; padding: 0 24px; }
.relative { position: relative; z-index: 1; }

/* ===== STICKY NAV ===== */
.nav {
  position: sticky; top: 0; z-index: 100;
  background: rgba(15, 23, 42, 0.6);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
  transition: background var(--transition-fast), box-shadow var(--transition-fast);
}
.nav.scrolled {
  background: rgba(15, 23, 42, 0.95);
  box-shadow: 0 4px 30px rgba(0, 0, 0, 0.3);
}
.nav-inner {
  display: flex; align-items: center; justify-content: space-between;
  height: 64px;
}
.nav-brand {
  font-size: 1.25rem; font-weight: 700;
  background: linear-gradient(135deg, var(--cyan), var(--violet));
  -webkit-background-clip: text; background-clip: text;
  -webkit-text-fill-color: transparent;
}
.nav-links {
  display: flex; gap: 32px; align-items: center;
  list-style: none;
}
.nav-links a {
  font-size: 0.9rem; font-weight: 500;
  color: var(--text-secondary);
  transition: color var(--transition-fast);
  position: relative;
}
.nav-links a:hover,
.nav-links a.active {
  color: var(--text-primary);
}
.nav-links a.active::after {
  content: '';
  position: absolute; bottom: -4px; left: 0; right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--cyan), var(--violet));
  border-radius: 1px;
}

/* Mobile menu toggle */
.nav-toggle {
  display: none;
  background: none; border: none; cursor: pointer;
  color: var(--text-primary); font-size: 1.5rem;
  padding: 4px;
}
.nav-toggle span {
  display: block; width: 24px; height: 2px;
  background: var(--text-primary);
  margin: 5px 0;
  transition: transform var(--transition-fast), opacity var(--transition-fast);
}

/* ===== HERO SECTION ===== */
.hero {
  padding: 120px 0 80px;
  text-align: center;
}
.hero h1 {
  font-size: clamp(2.5rem, 6vw, 4rem);
  font-weight: 900;
  letter-spacing: -0.02em;
  background: linear-gradient(135deg, var(--text-primary) 0%, var(--cyan-light) 50%, var(--violet-light) 100%);
  -webkit-background-clip: text; background-clip: text;
  -webkit-text-fill-color: transparent;
  margin-bottom: 16px;
  animation: fadeInUp 0.8s ease-out;
}
.hero .subtitle {
  font-size: clamp(1.1rem, 2.5vw, 1.4rem);
  color: var(--text-secondary);
  max-width: 600px; margin: 0 auto 24px;
  animation: fadeInUp 0.8s ease-out 0.15s both;
}
.hero .tagline {
  font-size: 0.95rem;
  color: var(--text-secondary);
  opacity: 0.7;
  max-width: 500px; margin: 0 auto;
  animation: fadeInUp 0.8s ease-out 0.3s both;
}

/* ===== FEATURED SECTION ===== */
.section-title {
  font-size: 1.5rem; font-weight: 700;
  margin-bottom: 32px;
  color: var(--text-emphasis);
}
.section-title span {
  background: linear-gradient(90deg, var(--cyan), var(--violet));
  -webkit-background-clip: text; background-clip: text;
  -webkit-text-fill-color: transparent;
}
.featured-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(360px, 1fr));
  gap: 24px;
  margin-bottom: 64px;
}

/* ===== CATEGORY FILTERS ===== */
.filters {
  display: flex; flex-wrap: wrap; gap: 10px;
  margin-bottom: 32px;
}
.filter-btn {
  padding: 8px 20px;
  border-radius: 9999px;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text-secondary);
  font-size: 0.85rem; font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-fast);
  font-family: inherit;
}
.filter-btn:hover {
  border-color: var(--border-hover);
  color: var(--text-primary);
  background: var(--bg-card);
}
.filter-btn.active {
  background: linear-gradient(135deg, rgba(6, 182, 212, 0.15), rgba(139, 92, 246, 0.15));
  border-color: var(--cyan);
  color: var(--cyan-light);
}

/* ===== PORTFOLIO GRID ===== */
.portfolio-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(340px, 1fr));
  gap: 20px;
  margin-bottom: 80px;
}

/* ===== CARD ===== */
.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 24px;
  transition: all var(--transition-medium);
  cursor: pointer;
  display: flex; flex-direction: column;
  text-decoration: none;
  position: relative;
  overflow: hidden;
}
.card::before {
  content: '';
  position: absolute; inset: 0;
  border-radius: 12px;
  padding: 1px;
  background: linear-gradient(135deg, transparent 40%, var(--cyan) 100%);
  -webkit-mask: linear-gradient(#fff 0 0) content-box, linear-gradient(#fff 0 0);
  -webkit-mask-composite: xor;
  mask-composite: exclude;
  opacity: 0;
  transition: opacity var(--transition-medium);
}
.card:hover {
  background: var(--bg-card-hover);
  transform: translateY(-4px);
  box-shadow: 0 12px 40px rgba(6, 182, 212, 0.08);
}
.card:hover::before {
  opacity: 1;
}
.card-badge {
  display: inline-block;
  padding: 4px 12px;
  border-radius: 9999px;
  font-size: 0.7rem; font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 12px;
  width: fit-content;
}
.card-badge.ai-ml { background: rgba(139, 92, 246, 0.15); color: var(--violet-light); }
.card-badge.research { background: rgba(6, 182, 212, 0.15); color: var(--cyan-light); }
.card-badge.simulations { background: rgba(245, 158, 11, 0.15); color: var(--amber-light); }
.card-badge.presentations { background: rgba(16, 185, 129, 0.15); color: var(--emerald); }
.card-badge.books { background: rgba(244, 63, 94, 0.15); color: var(--rose); }
.card-badge.tools { background: rgba(148, 163, 184, 0.15); color: var(--text-secondary); }
.card h3 {
  font-size: 1.1rem; font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 8px;
  transition: color var(--transition-fast);
}
.card:hover h3 {
  color: var(--cyan-light);
}
.card p {
  font-size: 0.875rem;
  color: var(--text-secondary);
  line-height: 1.5;
  flex: 1;
}
.card-arrow {
  display: flex; align-items: center; justify-content: flex-end;
  margin-top: 16px;
  color: var(--text-secondary);
  font-size: 0.8rem;
  transition: color var(--transition-fast);
}
.card:hover .card-arrow {
  color: var(--cyan);
}
.card-arrow svg {
  width: 16px; height: 16px;
  margin-left: 4px;
  transition: transform var(--transition-fast);
}
.card:hover .card-arrow svg {
  transform: translateX(4px);
}

/* Featured card variant */
.card.featured {
  border-color: rgba(6, 182, 212, 0.15);
}
.card.featured::before {
  opacity: 0.3;
}

/* ===== ABOUT PAGE ===== */
.about-hero {
  padding: 100px 0 40px;
  text-align: center;
}
.about-hero h1 {
  font-size: clamp(2rem, 5vw, 3rem);
  font-weight: 900;
  background: linear-gradient(135deg, var(--text-primary), var(--cyan-light));
  -webkit-background-clip: text; background-clip: text;
  -webkit-text-fill-color: transparent;
  margin-bottom: 12px;
}
.about-hero .subtitle {
  font-size: 1.05rem;
  color: var(--text-secondary);
  max-width: 700px; margin: 0 auto 20px;
}
.linkedin-link {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 10px 24px;
  border-radius: 9999px;
  border: 1px solid #0a66c2;
  color: #7fc1ff;
  font-size: 0.9rem; font-weight: 500;
  transition: all var(--transition-fast);
}
.linkedin-link:hover {
  background: rgba(10, 102, 194, 0.15);
  color: #a8d8ff;
}
.bio-section {
  max-width: 800px;
  margin: 0 auto 60px;
  padding: 0 24px;
}
.bio-section p {
  font-size: 1.1rem;
  color: var(--text-secondary);
  line-height: 1.8;
  margin-bottom: 16px;
}
.bifurcation-section {
  margin-bottom: 60px;
}
.bifurcation-section h2 {
  font-size: 1.5rem; font-weight: 700;
  color: var(--text-emphasis);
  margin-bottom: 24px;
  text-align: center;
}
.bifurcation-frame {
  width: 100%;
  height: 80vh;
  min-height: 500px;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: var(--bg-card);
}
.fullscreen-link {
  display: inline-flex; align-items: center; gap: 6px;
  margin-top: 16px;
  color: var(--cyan);
  font-size: 0.9rem; font-weight: 500;
  transition: color var(--transition-fast);
  text-align: center;
}
.fullscreen-link:hover {
  color: var(--cyan-light);
}

/* ===== FOOTER ===== */
.footer {
  border-top: 1px solid var(--border);
  padding: 40px 0;
  text-align: center;
}
.footer p {
  font-size: 0.85rem;
  color: var(--text-secondary);
}
.footer-links {
  display: flex; justify-content: center; gap: 24px;
  margin-top: 12px;
  list-style: none;
}
.footer-links a {
  color: var(--text-secondary);
  font-size: 0.85rem;
  transition: color var(--transition-fast);
}
.footer-links a:hover {
  color: var(--cyan);
}

/* ===== ANIMATIONS ===== */
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}
.fade-in {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.6s ease-out, transform 0.6s ease-out;
}
.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

/* ===== RESPONSIVE ===== */
@media (max-width: 768px) {
  .nav-links {
    display: none;
    position: absolute;
    top: 64px; left: 0; right: 0;
    background: rgba(15, 23, 42, 0.98);
    backdrop-filter: blur(16px);
    flex-direction: column;
    padding: 24px;
    gap: 20px;
    border-bottom: 1px solid var(--border);
  }
  .nav-links.open { display: flex; }
  .nav-toggle { display: block; }
  .hero { padding: 80px 0 60px; }
  .featured-grid,
  .portfolio-grid {
    grid-template-columns: 1fr;
  }
  .filters { justify-content: center; }
}

@media (max-width: 480px) {
  .container { padding: 0 16px; }
  .card { padding: 20px; }
}