:root {
    --bg: #0d1117;
    --surface: #161b22;
    --border: #30363d;
    --text: #e6edf3;
    --text-secondary: #8b949e;
    --accent: #58a6ff;
    --accent-hover: #79c0ff;
    --green: #3fb950;
    --orange: #d29922;
    --purple: #bc8cff;
    --red: #f85149;
}
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Noto Sans, Helvetica, Arial, sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    min-height: 100vh;
}
a { color: var(--accent); text-decoration: none; transition: color 0.2s; }
a:hover { color: var(--accent-hover); }

/* Navigation */
.nav {
    position: sticky; top: 0; z-index: 100;
    background: rgba(13, 17, 23, 0.85);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--border);
    padding: 0.75rem 2rem;
}
.nav-inner {
    max-width: 1100px; margin: 0 auto;
    display: flex; align-items: center; justify-content: space-between;
}
.nav-brand { font-weight: 700; font-size: 1.1rem; }
.nav-links { display: flex; gap: 1.5rem; list-style: none; }
.nav-links a { color: var(--text-secondary); font-size: 0.9rem; }
.nav-links a:hover { color: var(--text); }

/* Hero */
.hero {
    max-width: 1100px; margin: 0 auto;
    padding: 5rem 2rem 3rem;
    text-align: center;
}
.hero h1 { font-size: 2.8rem; font-weight: 800; margin-bottom: 0.5rem; }
.hero h1 span { color: var(--accent); }
.hero .subtitle {
    font-size: 1.2rem; color: var(--text-secondary);
    margin-bottom: 1.5rem;
}
.hero-bio {
    color: var(--text-secondary);
    max-width: 650px; margin: 0 auto 1.5rem;
    font-size: 0.95rem;
}
.hero-links { display: flex; gap: 1rem; justify-content: center; flex-wrap: wrap; }
.hero-links a {
    padding: 0.5rem 1.2rem; border-radius: 6px;
    font-size: 0.9rem; font-weight: 600;
    transition: all 0.2s;
}
.btn-primary { background: var(--accent); color: #fff !important; }
.btn-primary:hover { background: var(--accent-hover); }
.btn-outline { border: 1px solid var(--border); color: var(--text) !important; }
.btn-outline:hover { border-color: var(--accent); color: var(--accent) !important; }

/* Sections */
.section {
    max-width: 1100px; margin: 0 auto;
    padding: 3rem 2rem;
}
.section-title {
    font-size: 1.5rem; font-weight: 700;
    margin-bottom: 1.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 2px solid var(--border);
}
.section-title span { color: var(--accent); margin-right: 0.5rem; }

/* Project cards */
.projects-grid {
    display: grid; grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: 1.25rem;
}
.card {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 1.25rem;
    transition: border-color 0.2s, transform 0.2s;
    will-change: transform;
}
.card:hover { border-color: var(--accent); transform: translateY(-2px); }
.card-header { display: flex; align-items: center; gap: 0.5rem; margin-bottom: 0.5rem; }
.card-icon { font-size: 1.3rem; }
.card h3 { font-size: 1rem; font-weight: 600; }
.card h3 a { color: var(--text); }
.card h3 a:hover { color: var(--accent); }
.card p { font-size: 0.85rem; color: var(--text-secondary); margin-bottom: 0.75rem; line-height: 1.5; }
.card-tags { display: flex; flex-wrap: wrap; gap: 0.4rem; }
.tag {
    font-size: 0.7rem; padding: 0.15rem 0.5rem;
    border-radius: 99px;
    background: rgba(88, 166, 255, 0.1);
    color: var(--accent);
    border: 1px solid rgba(88, 166, 255, 0.2);
}
.card-links { display: flex; gap: 0.75rem; margin-top: 0.75rem; }
.card-links a { font-size: 0.8rem; color: var(--text-secondary); }
.card-links a:hover { color: var(--accent); }

/* Category labels */
.category { margin-bottom: 2rem; }
.category-label {
    font-size: 0.8rem; font-weight: 600; text-transform: uppercase;
    letter-spacing: 0.08em; color: var(--text-secondary);
    margin-bottom: 0.75rem;
}

/* Tech stack */
.tech-grid {
    display: flex; flex-wrap: wrap; gap: 0.5rem;
    justify-content: center;
}
.tech-badge {
    padding: 0.4rem 0.8rem;
    border-radius: 6px;
    font-size: 0.85rem; font-weight: 500;
    background: var(--surface);
    border: 1px solid var(--border);
    transition: border-color 0.2s;
}
.tech-badge:hover { border-color: var(--accent); }

/* Research */
.research-item {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 1.25rem;
    margin-bottom: 1rem;
}
.research-item h3 { font-size: 1rem; margin-bottom: 0.4rem; }
.research-item p { font-size: 0.85rem; color: var(--text-secondary); }
.highlight { color: var(--green); font-weight: 600; }

/* Stats */
.stats-grid {
    display: grid; grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
    gap: 1rem; text-align: center;
}
.stat {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 1.25rem 0.75rem;
}
.stat-number { font-size: 1.8rem; font-weight: 800; color: var(--accent); }
.stat-label { font-size: 0.8rem; color: var(--text-secondary); margin-top: 0.25rem; }

/* Footer */
.footer {
    max-width: 1100px; margin: 0 auto;
    padding: 2rem; text-align: center;
    border-top: 1px solid var(--border);
    color: var(--text-secondary); font-size: 0.85rem;
}
.footer-links { display: flex; gap: 1.5rem; justify-content: center; margin-bottom: 0.75rem; }

/* Responsive */
@media (max-width: 768px) {
    .hero h1 { font-size: 2rem; }
    .nav-links { gap: 1rem; }
    .projects-grid { grid-template-columns: 1fr; }
    .stats-grid { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 480px) {
    .nav-links { display: none; }
    .hero { padding: 3rem 1rem 2rem; }
    .section { padding: 2rem 1rem; }
}

/* Performance: defer rendering of off-screen sections */
#research, #tech, .footer {
    content-visibility: auto;
    contain-intrinsic-size: auto 500px;
}

/* Print styles */
@media print {
    .nav, .hero-links, .card-links, .footer-links { display: none; }
    body { background: #fff; color: #000; }
    a { color: #000; text-decoration: underline; }
    .card, .stat, .research-item { border: 1px solid #ccc; break-inside: avoid; }
    .section { padding: 1rem 0; }
}