:root {
  --bg: #0a0e14;
  --surface: #111827;
  --primary: #22d3ee;
  --secondary: #a78bfa;
  --text: #e5e7eb;
  --text-muted: #9ca3af;
  --border: #1f2937;
  --nav-bg: rgba(10, 14, 20, 0.85);
  --shadow: 0 4px 24px rgba(0, 0, 0, 0.35);
  --glow: 0 0 0 1px var(--primary), 0 0 20px rgba(34, 211, 238, 0.15);
  --radius: 12px;
  --max-w: 1100px;
  --font: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  color-scheme: dark;
}

[data-theme="light"] {
  --bg: #f8f9fa;
  --surface: #ffffff;
  --primary: #0e7490;
  --secondary: #7c3aed;
  --text: #1f2937;
  --text-muted: #6b7280;
  --border: #e5e7eb;
  --nav-bg: rgba(248, 249, 250, 0.85);
  --shadow: 0 4px 24px rgba(0, 0, 0, 0.08);
  --glow: 0 0 0 1px var(--primary), 0 0 16px rgba(8, 145, 178, 0.12);
  color-scheme: light;
}

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

html { scroll-padding-top: 72px; }

@media (prefers-reduced-motion: no-preference) {
  html { scroll-behavior: smooth; }
}

body {
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  transition: background-color 0.3s ease, color 0.3s ease;
}

img { max-width: 100%; display: block; }
a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }

.container { width: min(100% - 2rem, var(--max-w)); margin-inline: auto; }
.section { padding-block: 4.5rem; }

.section-title {
  font-size: clamp(1.5rem, 3vw, 2rem);
  margin-bottom: 2rem;
  color: var(--text);
}

.section-title::after {
  content: "";
  display: block;
  width: 48px;
  height: 3px;
  margin-top: 0.5rem;
  background: linear-gradient(90deg, var(--primary), var(--secondary));
  border-radius: 2px;
}

.reveal { opacity: 1; transform: none; }

@media (prefers-reduced-motion: no-preference) {
  .reveal {
    opacity: 0;
    transform: translateY(16px);
    transition: opacity 0.5s ease, transform 0.5s ease;
  }
  .reveal.reveal-visible { opacity: 1; transform: translateY(0); }
}

:focus-visible { outline: 2px solid var(--primary); outline-offset: 2px; }

.skip-link {
  position: absolute; left: -9999px; top: 0;
  background: var(--primary); color: var(--bg);
  padding: 0.5rem 1rem; z-index: 1000;
}
.skip-link:focus { left: 0; }

.navbar {
  position: sticky; top: 0; z-index: 100;
  background: var(--nav-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  transition: background-color 0.3s ease;
}

.nav-inner {
  display: flex; align-items: center; justify-content: space-between;
  min-height: 64px; gap: 1rem;
}

.nav-brand { font-size: 1.25rem; font-weight: 700; color: var(--text); text-decoration: none; }
.nav-brand .accent { color: var(--primary); }

.nav-menu { display: flex; align-items: center; gap: 1.5rem; }
.nav-links { display: flex; list-style: none; gap: 1.25rem; }
.nav-links a { color: var(--text-muted); font-size: 0.95rem; text-decoration: none; transition: color 0.2s ease; }
.nav-links a:hover, .nav-links a.active { color: var(--primary); }

.theme-toggle {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: 999px; width: 40px; height: 40px; cursor: pointer;
  display: grid; place-items: center; font-size: 1rem;
  transition: border-color 0.2s ease;
}
.theme-toggle:hover { border-color: var(--primary); }
.theme-icon--light { display: none; }
[data-theme="light"] .theme-icon--dark { display: none; }
[data-theme="light"] .theme-icon--light { display: inline; }

.nav-toggle { display: none; background: none; border: none; cursor: pointer; padding: 0.5rem; }
.hamburger, .hamburger::before, .hamburger::after {
  display: block; width: 22px; height: 2px; background: var(--text);
  position: relative; transition: transform 0.25s ease, opacity 0.25s ease;
}
.hamburger::before, .hamburger::after { content: ""; position: absolute; left: 0; }
.hamburger::before { top: -7px; }
.hamburger::after { top: 7px; }
.nav-toggle[aria-expanded="true"] .hamburger { background: transparent; }
.nav-toggle[aria-expanded="true"] .hamburger::before { top: 0; transform: rotate(45deg); }
.nav-toggle[aria-expanded="true"] .hamburger::after { top: 0; transform: rotate(-45deg); }

.footer {
  border-top: 1px solid var(--border); padding-block: 1.5rem;
  text-align: center; color: var(--text-muted); font-size: 0.9rem;
}

@media (max-width: 768px) {
  .nav-toggle { display: block; }
  .nav-menu {
    position: absolute; top: 64px; left: 0; right: 0;
    flex-direction: column; align-items: stretch;
    background: var(--surface); border-bottom: 1px solid var(--border);
    padding: 1rem; gap: 1rem; display: none;
  }
  .nav-menu.is-open { display: flex; }
  .nav-links { flex-direction: column; gap: 0.75rem; }
}

.hero { min-height: calc(100vh - 64px); display: flex; align-items: center; padding-block: 4rem; }
.hero-greeting { color: var(--primary); font-size: 1.1rem; margin-bottom: 0.75rem; font-family: var(--mono); }
.hero-title { font-size: clamp(1.75rem, 5vw, 3rem); line-height: 1.2; font-weight: 800; max-width: 18ch; margin-bottom: 1rem; }
.gradient-text {
  background: linear-gradient(90deg, var(--primary), var(--secondary));
  -webkit-background-clip: text; background-clip: text; color: transparent;
}
.hero-sub { color: var(--text-muted); font-size: 1.1rem; margin-bottom: 2rem; }
.hero-ctas { display: flex; flex-wrap: wrap; gap: 1rem; }

.btn {
  display: inline-flex; align-items: center; justify-content: center;
  padding: 0.75rem 1.5rem; border-radius: 8px; font-weight: 600; font-size: 1rem;
  text-decoration: none; transition: transform 0.2s ease, box-shadow 0.2s ease, background-color 0.2s ease;
  cursor: pointer; border: 2px solid transparent;
}
.btn:hover { text-decoration: none; transform: translateY(-2px); }
.btn-primary { background: var(--primary); color: var(--bg); }
.btn-primary:hover { box-shadow: 0 4px 16px rgba(34, 211, 238, 0.35); }
.btn-outline { border-color: var(--border); color: var(--text); background: transparent; }
.btn-outline:hover { border-color: var(--primary); color: var(--primary); }

.about-grid { display: grid; grid-template-columns: 1fr; gap: 2.5rem; }
@media (min-width: 768px) { .about-grid { grid-template-columns: 1fr 1.2fr; gap: 3rem; } }
.about-bio p { margin-bottom: 1rem; color: var(--text-muted); }
.about-bio strong { color: var(--text); }

.skills-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 1.25rem; }
@media (min-width: 900px) { .skills-grid { grid-template-columns: repeat(4, 1fr); } }
.skill-group { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 1rem; }
.skill-group h3 { font-size: 0.85rem; text-transform: uppercase; letter-spacing: 0.05em; color: var(--primary); margin-bottom: 0.75rem; }
.skill-group ul { list-style: none; }
.skill-group li { font-size: 0.9rem; color: var(--text-muted); padding-block: 0.2rem; }

.filter-pills { display: flex; flex-wrap: wrap; gap: 0.5rem; margin-bottom: 1.75rem; }
.pill {
  background: var(--surface); border: 1px solid var(--border); color: var(--text-muted);
  padding: 0.4rem 1rem; border-radius: 999px; font-size: 0.9rem; font-family: var(--mono);
  cursor: pointer; transition: all 0.2s ease;
}
.pill:hover { border-color: var(--primary); color: var(--primary); }
.pill.active { background: var(--primary); border-color: var(--primary); color: var(--bg); }

.projects-grid { display: grid; grid-template-columns: 1fr; gap: 1.25rem; }
@media (min-width: 640px) { .projects-grid { grid-template-columns: repeat(2, 1fr); } }
@media (min-width: 960px) { .projects-grid { grid-template-columns: repeat(3, 1fr); } }

.project-card {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 1.5rem; display: flex; flex-direction: column; gap: 0.75rem;
  transition: transform 0.25s ease, box-shadow 0.25s ease, border-color 0.25s ease, opacity 0.3s ease;
}
.project-card:hover { transform: translateY(-4px); border-color: var(--primary); box-shadow: var(--glow); }
.project-card.is-hidden { display: none; }
.project-icon { font-size: 1.75rem; }
.project-card h3 { font-size: 1.1rem; font-family: var(--mono); color: var(--text); }
.project-card p { font-size: 0.9rem; color: var(--text-muted); flex-grow: 1; }
.project-tags { display: flex; flex-wrap: wrap; gap: 0.35rem; }
.tag {
  font-size: 0.75rem; font-family: var(--mono); background: var(--bg);
  border: 1px solid var(--border); color: var(--secondary);
  padding: 0.15rem 0.5rem; border-radius: 4px;
}
.project-link { font-size: 0.9rem; font-weight: 600; color: var(--primary); text-decoration: none; margin-top: 0.25rem; }
.project-link:hover { text-decoration: underline; }
.filter-empty { text-align: center; color: var(--text-muted); padding: 2rem; }

.oss-intro { color: var(--text-muted); margin-bottom: 1rem; }
.oss-list { list-style: none; display: grid; gap: 0.75rem; }
.oss-list li {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 0.85rem 1.25rem;
  font-family: var(--mono); font-size: 0.95rem;
}
.oss-list a { color: var(--primary); }
.oss-note { color: var(--text-muted); font-size: 0.85rem; }

.coursework-grid { display: grid; gap: 0.75rem; }
.course-group {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 0.25rem 1.25rem;
}
.course-group summary {
  cursor: pointer; padding-block: 0.85rem; font-weight: 600;
  color: var(--text); list-style: none;
  display: flex; justify-content: space-between; align-items: center;
}
.course-group summary::-webkit-details-marker { display: none; }
.course-group summary::after { content: "+"; color: var(--primary); font-size: 1.25rem; }
.course-group[open] summary::after { content: "−"; }
.course-group ul { padding-bottom: 1rem; padding-left: 1.25rem; color: var(--text-muted); }
.course-group li { padding-block: 0.2rem; }

.contact-inner { text-align: center; }
.contact-lead { color: var(--text-muted); max-width: 40ch; margin-inline: auto; margin-bottom: 1.75rem; }
.contact-actions { display: flex; justify-content: center; flex-wrap: wrap; gap: 1rem; }