/* ===== RESET & BASE ===== */
*, *::before, *::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --bg-primary: #0f1117;
  --bg-secondary: #1a1d27;
  --bg-card: #222635;
  --accent: #6c9bff;
  --accent-hover: #8fb3ff;
  --text-primary: #e4e6ed;
  --text-secondary: #9ca0ad;
  --text-muted: #6b7080;
  --border: #2e3345;
  --font-body: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-heading: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --max-width: 960px;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-body);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.7;
  font-size: 16px;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

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

a:hover {
  color: var(--accent-hover);
}

img {
  max-width: 100%;
  height: auto;
}

/* ===== NAVIGATION ===== */
nav {
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 100;
}

nav .nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 2rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

nav .site-name {
  font-weight: 700;
  font-size: 1.15rem;
  color: var(--text-primary);
  letter-spacing: -0.01em;
}

nav .nav-links {
  list-style: none;
  display: flex;
  gap: 2rem;
}

nav .nav-links a {
  color: var(--text-secondary);
  font-size: 0.95rem;
  font-weight: 500;
  padding: 0.25rem 0;
  border-bottom: 2px solid transparent;
  transition: color 0.2s, border-color 0.2s;
}

nav .nav-links a:hover,
nav .nav-links a.active {
  color: var(--text-primary);
  border-bottom-color: var(--accent);
}

/* Mobile nav toggle */
.nav-toggle {
  display: none;
  background: none;
  border: none;
  color: var(--text-primary);
  font-size: 1.5rem;
  cursor: pointer;
}

/* ===== MAIN CONTENT ===== */
main {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 3rem 2rem;
  flex: 1;
  width: 100%;
}

/* ===== HEADINGS ===== */
h1 {
  font-family: var(--font-heading);
  font-size: 2rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 1.5rem;
  letter-spacing: -0.02em;
}

h2 {
  font-family: var(--font-heading);
  font-size: 1.4rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-top: 2.5rem;
  margin-bottom: 1rem;
  letter-spacing: -0.01em;
}

h3 {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 0.5rem;
}

/* ===== HOME PAGE: HERO ===== */
.hero {
  display: flex;
  gap: 3rem;
  align-items: flex-start;
  margin-bottom: 2rem;
}

.hero-photo {
  flex-shrink: 0;
}

.hero-photo img {
  width: 200px;
  height: 200px;
  object-fit: cover;
  border-radius: 12px;
  border: 2px solid var(--border);
}

.hero-text h1 {
  margin-bottom: 0.25rem;
}

.hero-text .subtitle {
  color: var(--text-secondary);
  font-size: 1.05rem;
  margin-bottom: 1.25rem;
}

.hero-text .bio {
  color: var(--text-secondary);
  line-height: 1.8;
}

/* ===== RESEARCH PAGE ===== */
.paper-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.paper-item {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1.25rem 1.5rem;
  transition: border-color 0.2s;
}

.paper-item:hover {
  border-color: var(--accent);
}

.paper-title {
  font-weight: 600;
  font-size: 1.05rem;
  color: var(--text-primary);
  margin-bottom: 0.3rem;
}

.paper-authors {
  color: var(--text-secondary);
  font-size: 0.9rem;
  margin-bottom: 0.3rem;
}

.paper-venue {
  color: var(--text-muted);
  font-size: 0.85rem;
  font-style: italic;
  margin-bottom: 0.75rem;
}

.paper-links {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
}

.paper-links a {
  font-size: 0.85rem;
  font-weight: 500;
  padding: 0.3rem 0.75rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  transition: background 0.2s, border-color 0.2s;
}

.paper-links a:hover {
  background: var(--bg-secondary);
  border-color: var(--accent);
}

/* Section labels for research grouping */
.section-year {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-top: 2rem;
  margin-bottom: 1rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--border);
}

/* ===== TEACHING PAGE ===== */
.course-list {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.course-item {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1.25rem 1.5rem;
}

.course-code {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.25rem;
}

.course-name {
  font-weight: 600;
  font-size: 1.05rem;
  color: var(--text-primary);
  margin-bottom: 0.3rem;
}

.course-details {
  color: var(--text-secondary);
  font-size: 0.9rem;
  line-height: 1.7;
}

/* ===== CONTACT PAGE ===== */
.contact-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
  margin-top: 1rem;
}

.contact-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1.5rem;
}

.contact-card h3 {
  margin-bottom: 0.75rem;
}

.contact-card p {
  color: var(--text-secondary);
  font-size: 0.95rem;
  line-height: 1.7;
}

/* ===== FOOTER ===== */
footer {
  border-top: 1px solid var(--border);
  text-align: center;
  padding: 1.5rem 2rem;
  color: var(--text-muted);
  font-size: 0.85rem;
}

/* ===== RESPONSIVE ===== */
@media (max-width: 700px) {
  .hero {
    flex-direction: column;
    align-items: center;
    text-align: center;
  }

  .hero-photo img {
    width: 160px;
    height: 160px;
  }

  .contact-grid {
    grid-template-columns: 1fr;
  }

  nav .nav-links {
    display: none;
    flex-direction: column;
    position: absolute;
    top: 64px;
    left: 0;
    right: 0;
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    padding: 1rem 2rem;
    gap: 1rem;
  }

  nav .nav-links.open {
    display: flex;
  }

  .nav-toggle {
    display: block;
  }
}