@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap');

:root {
  --primary-color: #2563eb;
  --primary-hover: #1d4ed8;
  --bg-color: #ffffff;
  --surface-color: #f8fafc;
  --text-main: #0f172a;
  --text-muted: #64748b;
  --border-color: #e2e8f0;
  
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --transition-speed: 0.3s;
}

[data-theme="dark"] {
  --primary-color: #60a5fa;
  --primary-hover: #93c5fd;
  --bg-color: #0f172a;
  --surface-color: #1e293b;
  --text-main: #f8fafc;
  --text-muted: #94a3b8;
  --border-color: #334155;
}

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

body {
  font-family: var(--font-sans);
  background-color: var(--bg-color);
  color: var(--text-main);
  line-height: 1.6;
  transition: background-color var(--transition-speed), color var(--transition-speed);
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

.container {
  width: 100%;
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 1.5rem;
}

/* Header & Navbar */
.site-header {
  border-bottom: 1px solid var(--border-color);
  background-color: var(--bg-color);
  position: sticky;
  top: 0;
  z-index: 1000;
  transition: background-color var(--transition-speed);
}

.navbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  height: 4.5rem;
}

.brand {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--text-main);
  text-decoration: none;
  letter-spacing: -0.025em;
}

.nav-links {
  display: flex;
  list-style: none;
  gap: 2rem;
  margin: 0;
  padding: 0;
}

.nav-links a {
  text-decoration: none;
  color: var(--text-muted);
  font-weight: 500;
  transition: color 0.2s;
}

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

.theme-toggle {
  background: none;
  border: none;
  color: var(--text-muted);
  cursor: pointer;
  padding: 0.5rem;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 50%;
  transition: background-color 0.2s, color 0.2s;
}

.theme-toggle:hover {
  background-color: var(--surface-color);
  color: var(--text-main);
}

.mobile-menu-btn {
  display: none;
  background: none;
  border: none;
  color: var(--text-main);
  cursor: pointer;
}

.nav-controls {
  display: flex;
  align-items: center;
  gap: 1rem;
}

/* Main Content Area */
main {
  flex: 1;
  padding: 4rem 0;
}

/* Typography */
h1 {
  font-size: 2.5rem;
  font-weight: 800;
  margin-bottom: 1.5rem;
  letter-spacing: -0.025em;
  color: var(--text-main);
}

h2 {
  font-size: 1.875rem;
  font-weight: 700;
  margin-top: 2.5rem;
  margin-bottom: 1rem;
}

h3 {
  font-size: 1.25rem;
  font-weight: 600;
  margin-top: 2rem;
  margin-bottom: 0.75rem;
}

p {
  margin-bottom: 1.25rem;
  font-size: 1.125rem;
  color: var(--text-muted);
}

a {
  color: var(--primary-color);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

/* Hero Section (Index) */
.hero {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  padding: 4rem 0;
}

.hero-avatar {
  width: 160px;
  height: 160px;
  border-radius: 50%;
  margin-bottom: 2rem;
  background-color: var(--surface-color);
  border: 4px solid var(--border-color);
  object-fit: cover;
}

.hero-title {
  font-size: 3rem;
  margin-bottom: 1rem;
  background: linear-gradient(to right, var(--primary-color), #8b5cf6);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.hero-subtitle {
  font-size: 1.25rem;
  max-width: 600px;
  margin: 0 auto 2rem auto;
}

.btn {
  display: inline-block;
  padding: 0.75rem 1.5rem;
  border-radius: 0.5rem;
  font-weight: 600;
  text-decoration: none;
  transition: all 0.2s;
}

.btn-primary {
  background-color: var(--primary-color);
  color: white;
  border: border-box;
}

.btn-primary:hover {
  background-color: var(--primary-hover);
  text-decoration: none;
  transform: translateY(-2px);
  box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
}

/* Cards (Publications / Courses) */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 2rem;
  margin-top: 2rem;
}

.card {
  background-color: var(--surface-color);
  border: 1px solid var(--border-color);
  border-radius: 0.75rem;
  padding: 1.5rem;
  transition: transform 0.2s, box-shadow 0.2s;
}

.card:hover {
  transform: translateY(-4px);
  box-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
}

.card h3 {
  margin-top: 0;
  margin-bottom: 0.5rem;
  color: var(--text-main);
}

.card .meta {
  font-size: 0.875rem;
  color: var(--primary-color);
  font-weight: 500;
  margin-bottom: 1rem;
  display: block;
}

.card p {
  font-size: 1rem;
  margin-bottom: 0;
}

/* Filtering & Labels */
.filter-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-bottom: 2rem;
}

.filter-btn {
  background-color: var(--surface-color);
  color: var(--text-main);
  border: 1px solid var(--border-color);
  padding: 0.5rem 1rem;
  border-radius: 2rem;
  font-size: 0.9rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s;
}

.filter-btn:hover {
  background-color: var(--border-color);
}

.filter-btn.active {
  background-color: var(--primary-color);
  color: white;
  border-color: var(--primary-color);
}

.card-labels {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-bottom: 0.75rem;
}

.label {
  background-color: #e0e7ff;
  color: var(--primary-color);
  border: 1px solid #c7d2fe;
  padding: 0.25rem 0.6rem;
  border-radius: 1rem;
  font-size: 0.725rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

[data-theme='dark'] .label {
    background-color: rgba(96, 165, 250, 0.15);
    color: var(--primary-color);
    border-color: rgba(96, 165, 250, 0.3);
}

/* Footer */
.site-footer {
  border-top: 1px solid var(--border-color);
  padding: 3rem 0;
  margin-top: auto;
  background-color: var(--surface-color);
}

.footer-content {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.footer-info h3 {
  margin: 0 0 0.5rem 0;
  font-size: 1.125rem;
}

.footer-info p {
  margin: 0;
  font-size: 0.875rem;
}

/* Mobile Responsiveness */
@media (max-width: 768px) {
  .nav-links {
    display: none;
    position: absolute;
    top: 4.5rem;
    left: 0;
    width: 100%;
    background-color: var(--bg-color);
    flex-direction: column;
    padding: 1rem;
    border-bottom: 1px solid var(--border-color);
    box-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
  }

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

  .mobile-menu-btn {
    display: block;
  }
}