/* ==========================================================================
   Alex Chen — Portfolio
   Dark, minimal, mobile-first. No frameworks.
   ========================================================================== */

:root {
    --bg: #0d1117;
    --bg-alt: #161b22;
    --bg-card: #161b22;
    --border: #30363d;
    --text: #e6edf3;
    --text-dim: #8b949e;
    --accent: #58a6ff;
    --accent-2: #3fb950;
    --code-bg: #1f2428;
    --max-width: 880px;
    --radius: 8px;
}

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

html { scroll-behavior: smooth; }

body {
    background: var(--bg);
    color: var(--text);
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    font-size: 16px;
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

code {
    background: var(--code-bg);
    padding: 0.15em 0.4em;
    border-radius: 4px;
    font-family: 'SFMono-Regular', Consolas, 'Liberation Mono', Menlo, monospace;
    font-size: 0.9em;
    color: var(--accent-2);
}

/* ---------- Layout ---------- */
.container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 20px;
}

/* ---------- Header / Nav ---------- */
.site-header {
    border-bottom: 1px solid var(--border);
    background: var(--bg);
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(8px);
}

.nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 56px;
}

.nav-brand {
    font-weight: 700;
    font-size: 1.05rem;
    color: var(--text);
}
.nav-brand:hover { text-decoration: none; }
.nav-brand .dot { color: var(--accent-2); }

.nav-links {
    display: flex;
    gap: 24px;
    list-style: none;
    align-items: center;
}

.nav-links a {
    color: var(--text-dim);
    font-size: 0.92rem;
    font-weight: 500;
}
.nav-links a:hover { color: var(--text); text-decoration: none; }

.nav-toggle {
    display: none;
    background: none;
    border: 1px solid var(--border);
    color: var(--text);
    border-radius: var(--radius);
    padding: 6px 10px;
    cursor: pointer;
    font-size: 1.1rem;
    line-height: 1;
}

/* ---------- Hero ---------- */
.hero {
    padding: 90px 0 60px;
    border-bottom: 1px solid var(--border);
}

.hero h1 {
    font-size: 2.4rem;
    font-weight: 800;
    letter-spacing: -0.02em;
    margin-bottom: 16px;
}

.hero h1 .accent { color: var(--accent); }

.hero .tagline {
    font-size: 1.15rem;
    color: var(--text-dim);
    max-width: 560px;
    margin-bottom: 28px;
}

.hero-cta {
    display: flex;
    gap: 12px;
    flex-wrap: wrap;
}

.btn {
    display: inline-block;
    padding: 10px 18px;
    border-radius: var(--radius);
    font-weight: 600;
    font-size: 0.92rem;
    border: 1px solid var(--border);
    transition: all 0.15s ease;
    cursor: pointer;
}
.btn-primary {
    background: var(--accent);
    color: #0d1117 !important;
    border-color: var(--accent);
}
.btn-primary:hover { background: #79b8ff; text-decoration: none; }
.btn-ghost {
    background: var(--bg-alt);
    color: var(--text);
}
.btn-ghost:hover { border-color: var(--text-dim); text-decoration: none; }

/* ---------- Section ---------- */
.section {
    padding: 56px 0;
    border-bottom: 1px solid var(--border);
}
.section:last-of-type { border-bottom: none; }

.section-title {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 8px;
    display: flex;
    align-items: center;
    gap: 10px;
}
.section-title .num {
    color: var(--accent-2);
    font-family: monospace;
    font-size: 1.1rem;
}

.section-sub {
    color: var(--text-dim);
    margin-bottom: 28px;
    font-size: 0.98rem;
}

/* ---------- Skills ---------- */
.skills-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 16px;
}
.skill-group {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 18px;
}
.skill-group h3 {
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-dim);
    margin-bottom: 10px;
}
.skill-tags {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}
.tag {
    background: var(--code-bg);
    border: 1px solid var(--border);
    color: var(--text);
    padding: 3px 9px;
    border-radius: 20px;
    font-size: 0.82rem;
}

/* ---------- Project cards ---------- */
.projects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 18px;
}

.card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 22px;
    transition: border-color 0.15s ease, transform 0.15s ease;
}
.card:hover {
    border-color: var(--text-dim);
    transform: translateY(-2px);
}

.card-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: 12px;
}
.card-title {
    font-size: 1.05rem;
    font-weight: 700;
}
.card-icon {
    color: var(--text-dim);
    font-size: 1.2rem;
}
.card-desc {
    color: var(--text-dim);
    font-size: 0.9rem;
    margin-bottom: 14px;
}
.card-meta {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
}
.card-meta .tag { font-size: 0.76rem; padding: 2px 8px; }

/* ---------- About ---------- */
.prose {
    max-width: 680px;
}
.prose p { margin-bottom: 16px; color: var(--text); }
.prose p.dim { color: var(--text-dim); }
.prose ul { margin: 0 0 16px 20px; }
.prose li { margin-bottom: 6px; }

/* ---------- Footer ---------- */
.site-footer {
    border-top: 1px solid var(--border);
    padding: 32px 0;
    color: var(--text-dim);
    font-size: 0.88rem;
}
.footer-grid {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 12px;
}
.footer-links { display: flex; gap: 18px; }
.footer-links a { color: var(--text-dim); }
.footer-links a:hover { color: var(--text); }

/* ---------- Mobile ---------- */
@media (max-width: 640px) {
    .hero { padding: 60px 0 40px; }
    .hero h1 { font-size: 1.9rem; }
    .hero .tagline { font-size: 1.02rem; }
    .section { padding: 40px 0; }
    .section-title { font-size: 1.3rem; }

    .nav-toggle { display: block; }
    .nav-links {
        display: none;
        position: absolute;
        top: 56px;
        left: 0;
        right: 0;
        background: var(--bg);
        border-bottom: 1px solid var(--border);
        flex-direction: column;
        gap: 0;
        padding: 8px 20px 16px;
    }
    .nav-links.open { display: flex; }
    .nav-links li { width: 100%; }
    .nav-links a {
        display: block;
        padding: 12px 0;
        border-bottom: 1px solid var(--border);
    }
    .nav-links li:last-child a { border-bottom: none; }
}