/* ============================================================
   MathonAI Team — Design System
   Style: Clean, Light, Minimal, Academic
   Palette: CMU Red-Black + White/Light Gray
   ============================================================ */

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

/* --- CSS Custom Properties --- */
:root {
  /* Colors — CMU Red-Black */
  --color-bg:           #f8f7f5;
  --color-surface:      #ffffff;
  --color-surface-alt:  #f3f1ee;
  --color-border:       #e0ddd8;
  --color-border-light: #eae7e3;

  --color-primary:      #C41230;
  --color-primary-light:#d63a54;
  --color-primary-dark: #9e0e26;
  --color-primary-bg:   #fdf0f2;

  --color-text:         #1a1a1a;
  --color-text-secondary: #4a4a4a;
  --color-text-muted:   #7a7a7a;

  --color-accent:       #C41230;
  --color-accent-green: #27ae60;
  --color-accent-amber: #f39c12;

  /* Typography */
  --font-sans:    'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-serif:   'Playfair Display', Georgia, 'Times New Roman', serif;

  --text-xs:   0.75rem;
  --text-sm:   0.875rem;
  --text-base: 1rem;
  --text-lg:   1.125rem;
  --text-xl:   1.25rem;
  --text-2xl:  1.5rem;
  --text-3xl:  1.875rem;
  --text-4xl:  2.25rem;
  --text-5xl:  3rem;

  /* Spacing */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;
  --space-20: 5rem;
  --space-24: 6rem;

  /* Layout */
  --max-width:  1200px;
  --nav-height: 72px;

  /* Effects */
  --shadow-sm:  0 1px 3px rgba(0,0,0,0.06), 0 1px 2px rgba(0,0,0,0.04);
  --shadow-md:  0 4px 12px rgba(0,0,0,0.07), 0 2px 4px rgba(0,0,0,0.04);
  --shadow-lg:  0 10px 30px rgba(0,0,0,0.08), 0 4px 8px rgba(0,0,0,0.04);
  --shadow-card: 0 2px 8px rgba(0,0,0,0.05);

  --radius-sm:  6px;
  --radius-md:  10px;
  --radius-lg:  16px;
  --radius-xl:  24px;
  --radius-full: 9999px;

  --transition: 0.3s cubic-bezier(0.25, 0.46, 0.45, 0.94);
}

/* --- Reset & Base --- */
*, *::before, *::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-sans);
  color: var(--color-text);
  background-color: var(--color-bg);
  line-height: 1.7;
  min-height: 100vh;
}

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

a:hover {
  color: var(--color-primary-dark);
}

img {
  max-width: 100%;
  display: block;
}

/* --- Layout --- */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-8);
}

.page {
  display: none;
  animation: fadeIn 0.4s ease-out;
}

.page.active {
  display: block;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(12px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* ============================================================
   NAVIGATION
   ============================================================ */
.navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: rgba(255,255,255,0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border-light);
  z-index: 1000;
  transition: box-shadow var(--transition);
}

.navbar.scrolled {
  box-shadow: var(--shadow-sm);
}

.navbar .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  font-family: var(--font-serif);
  font-size: var(--text-xl);
  font-weight: 600;
  color: var(--color-text);
  cursor: pointer;
  transition: color var(--transition);
}

.nav-logo:hover {
  color: var(--color-primary);
}

.nav-logo-icon {
  width: 36px;
  height: 36px;
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-light));
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-size: var(--text-lg);
  font-family: var(--font-serif);
  font-weight: 700;
}

.nav-links {
  display: flex;
  gap: var(--space-1);
  list-style: none;
}

.nav-links li a {
  display: block;
  padding: var(--space-2) var(--space-5);
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--color-text-secondary);
  border-radius: var(--radius-sm);
  transition: all var(--transition);
  letter-spacing: 0.02em;
}

.nav-links li a:hover {
  color: var(--color-primary);
  background: var(--color-primary-bg);
}

.nav-links li a.active {
  color: var(--color-primary);
  background: var(--color-primary-bg);
  font-weight: 600;
}

/* Mobile menu toggle */
.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  cursor: pointer;
  padding: var(--space-2);
}

.nav-toggle span {
  width: 22px;
  height: 2px;
  background: var(--color-text);
  border-radius: 2px;
  transition: all var(--transition);
}

/* ============================================================
   HERO SECTION (About page)
   ============================================================ */
.hero {
  padding: calc(var(--nav-height) + var(--space-16)) 0 var(--space-16);
  background: linear-gradient(170deg, #fdf0f2 0%, #f8f7f5 50%, #ffffff 100%);
  text-align: center;
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: -50%;
  right: -20%;
  width: 600px;
  height: 600px;
  background: radial-gradient(circle, rgba(196,18,48,0.04) 0%, transparent 70%);
  border-radius: 50%;
}

.hero::after {
  content: '';
  position: absolute;
  bottom: -30%;
  left: -10%;
  width: 400px;
  height: 400px;
  background: radial-gradient(circle, rgba(196,18,48,0.03) 0%, transparent 70%);
  border-radius: 50%;
}

.hero-content {
  position: relative;
  z-index: 1;
}

.hero h1 {
  font-family: var(--font-serif);
  font-size: var(--text-5xl);
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: var(--space-4);
  letter-spacing: -0.02em;
}

.hero .tagline {
  font-size: var(--text-xl);
  color: var(--color-text-secondary);
  font-weight: 300;
  letter-spacing: 0.04em;
}

/* ============================================================
   PAGE HEADER (for non-About pages)
   ============================================================ */
.page-header {
  padding: calc(var(--nav-height) + var(--space-12)) 0 var(--space-10);
  background: linear-gradient(170deg, #fdf0f2 0%, #f8f7f5 100%);
}

.page-header h1 {
  font-family: var(--font-serif);
  font-size: var(--text-4xl);
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: var(--space-2);
}

.page-header p {
  font-size: var(--text-lg);
  color: var(--color-text-secondary);
  max-width: 600px;
}

/* ============================================================
   SECTIONS
   ============================================================ */
.section {
  padding: var(--space-16) 0;
}

.section-alt {
  background: var(--color-surface);
}

.section-title {
  font-family: var(--font-serif);
  font-size: var(--text-3xl);
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: var(--space-2);
}

.section-subtitle {
  font-size: var(--text-base);
  color: var(--color-primary);
  font-weight: 500;
  margin-bottom: var(--space-10);
}

/* ============================================================
   ABOUT PAGE — Intro
   ============================================================ */
.about-intro {
  max-width: 800px;
  margin: 0 auto;
  text-align: center;
  padding: var(--space-16) 0;
}

.about-intro p {
  font-size: var(--text-lg);
  color: var(--color-text-secondary);
  line-height: 1.9;
}

/* ============================================================
   ABOUT PAGE — Research Cards
   ============================================================ */
.research-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--space-6);
  margin-top: var(--space-8);
}

.research-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  padding: var(--space-8) var(--space-6);
  text-align: center;
  transition: all var(--transition);
  position: relative;
  overflow: hidden;
}

.research-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--color-primary), var(--color-primary-light));
  transform: scaleX(0);
  transition: transform var(--transition);
}

.research-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
  border-color: var(--color-primary-bg);
}

.research-card:hover::before {
  transform: scaleX(1);
}

.research-card-icon {
  width: 56px;
  height: 56px;
  margin: 0 auto var(--space-5);
  background: var(--color-primary-bg);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 24px;
  color: var(--color-primary);
}

.research-card h3 {
  font-size: var(--text-base);
  font-weight: 600;
  margin-bottom: var(--space-3);
  color: var(--color-text);
}

.research-card p {
  font-size: var(--text-sm);
  color: var(--color-text-secondary);
  line-height: 1.6;
}

/* ============================================================
   NEWS PAGE
   ============================================================ */
.news-list {
  max-width: 800px;
  padding: var(--space-12) 0 var(--space-16);
}

.news-item {
  display: flex;
  gap: var(--space-6);
  padding: var(--space-6) 0;
  border-bottom: 1px solid var(--color-border-light);
  transition: all var(--transition);
}

.news-item:last-child {
  border-bottom: none;
}

.news-item:hover {
  padding-left: var(--space-4);
}

.news-date {
  flex-shrink: 0;
  width: 132px;
}

.news-date-tag {
  display: inline-block;
  padding: var(--space-1) var(--space-3);
  background: var(--color-primary-bg);
  color: var(--color-primary);
  font-size: var(--text-xs);
  font-weight: 600;
  border-radius: var(--radius-sm);
  letter-spacing: 0.03em;
  white-space: nowrap;
}

.news-content {
  flex: 1;
  border-left: 3px solid var(--color-primary-bg);
  padding-left: var(--space-6);
  transition: border-color var(--transition);
}

.news-item:hover .news-content {
  border-color: var(--color-primary);
}

.news-content h3 {
  font-size: var(--text-lg);
  font-weight: 600;
  margin-bottom: var(--space-2);
  color: var(--color-text);
}

.news-content p {
  font-size: var(--text-sm);
  color: var(--color-text-secondary);
  line-height: 1.7;
}

/* ============================================================
   PUBLICATIONS PAGE
   ============================================================ */
.pub-list {
  padding-top: var(--space-10);
  padding-bottom: var(--space-16);
}

.pub-group + .pub-group {
  margin-top: var(--space-12);
}

.pub-group-title {
  font-family: var(--font-serif);
  font-size: var(--text-2xl);
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: var(--space-4);
}

.pub-group-list {
  border-top: 1px solid var(--color-border-light);
}

.pub-item {
  padding: var(--space-6) 0;
  border-bottom: 1px solid var(--color-border-light);
  transition: all var(--transition);
}

.pub-item:hover {
  padding-left: var(--space-4);
}

.pub-item:last-child {
  border-bottom: none;
}

.pub-title {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: var(--space-2);
  line-height: 1.5;
}

.pub-authors {
  font-size: var(--text-sm);
  color: var(--color-text-secondary);
  margin-bottom: var(--space-1);
}

.pub-venue {
  font-size: var(--text-sm);
  color: var(--color-primary);
  font-style: italic;
  margin-bottom: var(--space-3);
}

.pub-links {
  display: flex;
  gap: var(--space-3);
}

.pub-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-1) var(--space-3);
  font-size: var(--text-xs);
  font-weight: 600;
  color: var(--color-primary);
  background: var(--color-primary-bg);
  border-radius: var(--radius-sm);
  transition: all var(--transition);
  letter-spacing: 0.03em;
}

.pub-link:hover {
  background: var(--color-primary);
  color: white;
}

/* ============================================================
   PROJECT PAGE
   ============================================================ */
.project-grid {
  display: block;
  padding: var(--space-10) 0 var(--space-16);
  border-top: 1px solid var(--color-border-light);
}

.project-card {
  padding: var(--space-6) 0;
  border-bottom: 1px solid var(--color-border-light);
  transition: all var(--transition);
}

.project-card:hover {
  padding-left: var(--space-4);
}

.project-label {
  display: inline-block;
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--color-primary);
  font-style: italic;
  margin-bottom: var(--space-3);
}

.project-card h3 {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: var(--space-2);
  line-height: 1.5;
}

.project-card p {
  font-size: var(--text-sm);
  color: var(--color-text-secondary);
  line-height: 1.7;
  margin-bottom: var(--space-3);
}

.project-authors {
  font-size: var(--text-sm);
  color: var(--color-text);
  margin-bottom: var(--space-4);
}

.project-authors strong {
  color: var(--color-primary);
  font-weight: 600;
}

.project-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--color-primary);
  transition: gap var(--transition);
}

.project-link:hover {
  gap: var(--space-3);
}

/* ============================================================
   COURSE PAGE
   ============================================================ */
.course-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--space-6);
  padding: var(--space-10) 0 var(--space-16);
}

.course-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  padding: var(--space-8);
  transition: all var(--transition);
  position: relative;
}

.course-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
}

.course-code {
  display: inline-block;
  font-size: var(--text-xs);
  font-weight: 700;
  color: var(--color-primary);
  background: var(--color-primary-bg);
  padding: var(--space-1) var(--space-3);
  border-radius: var(--radius-sm);
  letter-spacing: 0.05em;
  margin-bottom: var(--space-3);
}

.course-card h3 {
  font-family: var(--font-serif);
  font-size: var(--text-2xl);
  font-weight: 600;
  margin-bottom: var(--space-3);
  color: var(--color-text);
}

.course-meta {
  display: flex;
  gap: var(--space-4);
  margin-bottom: var(--space-4);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

.course-meta span {
  display: flex;
  align-items: center;
  gap: var(--space-1);
}

.course-card p {
  font-size: var(--text-sm);
  color: var(--color-text-secondary);
  line-height: 1.7;
  margin-bottom: var(--space-5);
}

.course-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--color-primary);
  transition: gap var(--transition);
}

.course-link:hover {
  gap: var(--space-3);
}

/* ============================================================
   TEAM PAGE
   ============================================================ */
.team-section {
  padding: var(--space-10) 0;
}

.team-section:first-of-type {
  padding-top: var(--space-12);
}

.team-role-title {
  font-family: var(--font-serif);
  font-size: var(--text-2xl);
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: var(--space-6);
  padding-bottom: var(--space-3);
  border-bottom: 2px solid var(--color-primary-bg);
}

.team-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--space-6);
}

.team-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  padding: var(--space-6) var(--space-8);
  display: flex;
  align-items: center;
  gap: var(--space-6);
  transition: all var(--transition);
  min-height: 120px;
}

.team-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
  border-color: var(--color-primary-bg);
}

.team-avatar {
  width: 80px;
  height: 80px;
  border-radius: 50%;
  overflow: hidden;
  flex-shrink: 0;
  border: 2px solid var(--color-border-light);
}

.team-avatar img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.team-info h3 {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: var(--space-1);
}

.team-info .team-role {
  font-size: var(--text-sm);
  color: var(--color-primary);
  font-weight: 500;
  margin-bottom: var(--space-2);
}

.team-site-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  font-size: var(--text-xs);
  font-weight: 600;
  color: var(--color-primary);
  margin-bottom: var(--space-2);
}

.team-site-link:hover {
  color: var(--color-primary-dark);
}

.team-info .team-interest {
  font-size: var(--text-xs);
  color: var(--color-text-muted);
  line-height: 1.5;
}

/* ============================================================
   FOOTER
   ============================================================ */
.footer {
  background: var(--color-surface);
  border-top: 1px solid var(--color-border-light);
  padding: var(--space-10) 0;
  margin-top: var(--space-8);
}

.footer-content {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: var(--space-8);
}

.footer-brand {
  flex: 1;
}

.footer-brand h3 {
  font-family: var(--font-serif);
  font-size: var(--text-xl);
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: var(--space-2);
}

.footer-brand p {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

.footer-links h4 {
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: var(--space-3);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.footer-links ul {
  list-style: none;
}

.footer-links ul li {
  margin-bottom: var(--space-2);
}

.footer-links ul li a {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

.footer-links ul li a:hover {
  color: var(--color-primary);
}

.footer-bottom {
  border-top: 1px solid var(--color-border-light);
  margin-top: var(--space-8);
  padding-top: var(--space-6);
  text-align: center;
  font-size: var(--text-xs);
  color: var(--color-text-muted);
}

/* ============================================================
   RESPONSIVE
   ============================================================ */
@media (max-width: 1024px) {
  .research-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 768px) {
  .nav-links {
    display: none;
    position: absolute;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background: var(--color-surface);
    flex-direction: column;
    padding: var(--space-4);
    border-bottom: 1px solid var(--color-border);
    box-shadow: var(--shadow-md);
  }

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

  .nav-toggle {
    display: flex;
  }

  .hero h1 {
    font-size: var(--text-3xl);
  }

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

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

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

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

  .news-item {
    flex-direction: column;
    gap: var(--space-3);
  }

  .footer-content {
    flex-direction: column;
  }
}

@media (max-width: 480px) {
  .container {
    padding: 0 var(--space-4);
  }

  .hero h1 {
    font-size: var(--text-2xl);
  }

  .page-header h1 {
    font-size: var(--text-2xl);
  }
}