/* ===========================
   Root Variables & Reset
   =========================== */
:root {
  --primary-color: #2563eb;
  --primary-dark: #1e40af;
  --primary-light: #3b82f6;
  --secondary-color: #64748b;
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #64748b;
  --bg-primary: #ffffff;
  --bg-secondary: #f8fafc;
  --bg-tertiary: #f1f5f9;
  --border-color: #e2e8f0;
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
  --radius-sm: 0.375rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --radius-xl: 1rem;
  --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-base: 300ms cubic-bezier(0.4, 0, 0.2, 1);
}

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

html {
  scroll-behavior: smooth;
}

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

/* ===========================
   Typography
   =========================== */
h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: 1.2;
  color: var(--text-primary);
}

h1 {
  font-size: 3.5rem;
  font-weight: 700;
}

h2 {
  font-size: 2.5rem;
}

h3 {
  font-size: 1.5rem;
}

p {
  margin-bottom: 1rem;
}

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

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

strong {
  font-weight: 600;
  color: var(--text-primary);
}

/* ===========================
   Container & Layout
   =========================== */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 2rem;
}

.section {
  padding: 5rem 0;
}

.section-title {
  font-size: 2.5rem;
  font-weight: 700;
  text-align: center;
  margin-bottom: 3rem;
  color: var(--text-primary);
  position: relative;
}

.section-title::after {
  content: '';
  display: block;
  width: 60px;
  height: 4px;
  background: linear-gradient(90deg, var(--primary-color), var(--primary-light));
  margin: 1rem auto 0;
  border-radius: 2px;
}

/* ===========================
   Navigation
   =========================== */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  box-shadow: var(--shadow-sm);
  transition: all var(--transition-base);
}

.nav.scrolled {
  box-shadow: var(--shadow-md);
}

.nav-content {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1rem 0;
}

.logo {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--text-primary);
  transition: color var(--transition-fast);
}

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

.nav-links {
  display: flex;
  gap: 2rem;
  align-items: center;
}

.nav-links a {
  color: var(--text-secondary);
  font-weight: 500;
  font-size: 0.95rem;
  position: relative;
  transition: color var(--transition-fast);
}

.nav-links a::after {
  content: '';
  position: absolute;
  bottom: -4px;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--primary-color);
  transition: width var(--transition-base);
}

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

.nav-links a:hover::after {
  width: 100%;
}

.mobile-menu-btn {
  display: none;
  flex-direction: column;
  gap: 4px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.5rem;
}

.mobile-menu-btn span {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--text-primary);
  transition: all var(--transition-base);
}

/* ===========================
   Hero Section
   =========================== */
.hero {
  padding-top: 8rem;
  padding-bottom: 6rem;
  background: linear-gradient(135deg, #f8fafc 0%, #e0e7ff 100%);
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: 
    radial-gradient(circle at 20% 50%, rgba(99, 102, 241, 0.05) 0%, transparent 50%),
    radial-gradient(circle at 80% 80%, rgba(37, 99, 235, 0.05) 0%, transparent 50%);
  pointer-events: none;
}

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

.hero-text {
  max-width: 800px;
}

.greeting {
  display: block;
  font-size: 1.25rem;
  font-weight: 500;
  color: var(--primary-color);
  margin-bottom: 0.5rem;
}

.name {
  display: block;
  font-size: 3.5rem;
  font-weight: 700;
  background: linear-gradient(135deg, var(--primary-dark) 0%, var(--primary-color) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: 0.5rem;
}

.hero-subtitle {
  font-size: 1.75rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 0.5rem;
}

.hero-focus {
  font-size: 1.125rem;
  color: var(--text-secondary);
  margin-bottom: 1.5rem;
}

.hero-description {
  font-size: 1.125rem;
  color: var(--text-secondary);
  margin-bottom: 2rem;
  line-height: 1.8;
}

.hero-buttons {
  display: flex;
  gap: 1rem;
  margin-bottom: 2rem;
  flex-wrap: wrap;
}

.btn {
  display: inline-block;
  padding: 0.875rem 1.75rem;
  border-radius: var(--radius-md);
  font-weight: 600;
  font-size: 1rem;
  transition: all var(--transition-base);
  border: 2px solid transparent;
}

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

.btn-primary:hover {
  background: var(--primary-dark);
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}

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

.btn-secondary:hover {
  background: var(--primary-color);
  color: white;
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.hero-meta {
  display: flex;
  gap: 1rem;
  align-items: center;
  font-size: 0.95rem;
  color: var(--text-secondary);
}

.separator {
  color: var(--border-color);
}

/* ===========================
   Research Focus Section
   =========================== */
.research-focus {
  background: var(--bg-primary);
}

.research-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 2rem;
}

.research-card {
  padding: 2rem;
  background: white;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
  transition: all var(--transition-base);
}

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

.research-icon {
  font-size: 2.5rem;
  margin-bottom: 1rem;
}

.research-card h3 {
  font-size: 1.25rem;
  margin-bottom: 0.75rem;
  color: var(--text-primary);
}

.research-card p {
  color: var(--text-secondary);
  font-size: 0.95rem;
  line-height: 1.6;
  margin-bottom: 0;
}

/* ===========================
   Publications Section
   =========================== */
.publications-section {
  background: var(--bg-secondary);
}

.publications {
  display: flex;
  flex-direction: column;
  gap: 2rem;
  max-width: 900px;
  margin: 0 auto;
}

.publication-card {
  display: flex;
  gap: 2rem;
  padding: 2rem;
  background: white;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
  transition: all var(--transition-base);
}

.publication-card:hover {
  box-shadow: var(--shadow-lg);
  border-color: var(--primary-color);
}

.pub-year {
  flex-shrink: 0;
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary-color);
  width: 80px;
}

.pub-content {
  flex: 1;
}

.pub-title {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
  line-height: 1.4;
}

.pub-venue {
  font-size: 0.95rem;
  color: var(--primary-color);
  font-weight: 600;
  margin-bottom: 0.75rem;
}

.pub-description {
  color: var(--text-secondary);
  line-height: 1.7;
  margin-bottom: 1rem;
}

.pub-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.tag {
  display: inline-block;
  padding: 0.375rem 0.875rem;
  background: var(--bg-secondary);
  color: var(--primary-color);
  font-size: 0.85rem;
  font-weight: 500;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
}

/* ===========================
   Experience Section
   =========================== */
.experience-section {
  background: var(--bg-primary);
}

.timeline {
  max-width: 900px;
  margin: 0 auto;
  position: relative;
}

.timeline::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 2px;
  background: var(--border-color);
}

.timeline-item {
  position: relative;
  padding-left: 3rem;
  padding-bottom: 3rem;
}

.timeline-item:last-child {
  padding-bottom: 0;
}

.timeline-marker {
  position: absolute;
  left: -6px;
  top: 0;
  width: 14px;
  height: 14px;
  border-radius: 50%;
  background: var(--primary-color);
  border: 3px solid white;
  box-shadow: 0 0 0 2px var(--primary-color);
}

.timeline-content {
  background: white;
  padding: 2rem;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
  transition: all var(--transition-base);
}

.timeline-content:hover {
  box-shadow: var(--shadow-lg);
  border-color: var(--primary-color);
}

.timeline-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: 1rem;
  gap: 1rem;
  flex-wrap: wrap;
}

.timeline-title {
  font-size: 1.25rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 0.25rem;
}

.timeline-company {
  font-size: 1rem;
  color: var(--primary-color);
  font-weight: 500;
}

.timeline-meta {
  text-align: right;
  flex-shrink: 0;
}

.timeline-date {
  display: block;
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-secondary);
}

.timeline-location {
  display: block;
  font-size: 0.875rem;
  color: var(--text-muted);
  margin-top: 0.25rem;
}

.timeline-description {
  list-style: none;
  padding-left: 0;
}

.timeline-description li {
  position: relative;
  padding-left: 1.5rem;
  margin-bottom: 0.75rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

.timeline-description li:last-child {
  margin-bottom: 0;
}

.timeline-description li::before {
  content: '→';
  position: absolute;
  left: 0;
  color: var(--primary-color);
  font-weight: 600;
}

/* ===========================
   Education Section
   =========================== */
.education-section {
  background: var(--bg-secondary);
}

.education-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
  gap: 2rem;
  max-width: 900px;
  margin: 0 auto;
}

.education-card {
  display: flex;
  gap: 2rem;
  padding: 2rem;
  background: white;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
  transition: all var(--transition-base);
}

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

.edu-year {
  flex-shrink: 0;
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary-color);
  width: 80px;
}

.edu-content {
  flex: 1;
}

.edu-degree {
  font-size: 1.25rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 0.25rem;
}

.edu-specialization {
  font-size: 0.95rem;
  color: var(--primary-color);
  font-weight: 500;
  margin-bottom: 0.5rem;
}

.edu-school {
  font-size: 1rem;
  color: var(--text-secondary);
  margin-bottom: 0.75rem;
}

.edu-courses,
.edu-honors {
  font-size: 0.9rem;
  color: var(--text-muted);
  line-height: 1.6;
}

/* ===========================
   Skills Section
   =========================== */
.skills-section {
  background: var(--bg-primary);
}

.skills-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 2rem;
  max-width: 1000px;
  margin: 0 auto;
}

.skill-category {
  padding: 2rem;
  background: white;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
  transition: all var(--transition-base);
}

.skill-category:hover {
  box-shadow: var(--shadow-lg);
  border-color: var(--primary-color);
}

.skill-category-title {
  font-size: 1.25rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 1.25rem;
  padding-bottom: 0.75rem;
  border-bottom: 2px solid var(--border-color);
}

.skill-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.skill-tag {
  display: inline-block;
  padding: 0.5rem 1rem;
  background: var(--bg-secondary);
  color: var(--text-secondary);
  font-size: 0.9rem;
  font-weight: 500;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  transition: all var(--transition-fast);
}

.skill-tag:hover {
  background: var(--primary-color);
  color: white;
  border-color: var(--primary-color);
  transform: translateY(-2px);
}

/* ===========================
   Contact Section
   =========================== */
.contact-section {
  background: var(--bg-secondary);
}

.contact-content {
  max-width: 800px;
  margin: 0 auto;
  text-align: center;
}

.contact-intro {
  font-size: 1.125rem;
  color: var(--text-secondary);
  margin-bottom: 3rem;
  line-height: 1.8;
}

.contact-methods {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1.5rem;
}

.contact-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
  padding: 2rem 1.5rem;
  background: white;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
  transition: all var(--transition-base);
  text-align: center;
}

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

.contact-icon {
  font-size: 2.5rem;
}

.contact-card h3 {
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 0.25rem;
}

.contact-card p {
  font-size: 0.95rem;
  color: var(--text-secondary);
  margin-bottom: 0;
  word-break: break-word;
}

/* ===========================
   Footer
   =========================== */
.footer {
  background: var(--text-primary);
  color: var(--bg-secondary);
  padding: 2rem 0;
  text-align: center;
}

.footer p {
  margin-bottom: 0.5rem;
  font-size: 0.95rem;
}

.footer-note {
  font-size: 0.875rem;
  color: var(--text-muted);
}

/* ===========================
   Responsive Design
   =========================== */
@media (max-width: 768px) {
  .container {
    padding: 0 1.5rem;
  }

  .section {
    padding: 3rem 0;
  }

  .section-title {
    font-size: 2rem;
  }

  .nav-links {
    display: none;
  }

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

  .hero {
    padding-top: 6rem;
    padding-bottom: 4rem;
  }

  .name {
    font-size: 2.5rem;
  }

  .hero-subtitle {
    font-size: 1.5rem;
  }

  .hero-focus {
    font-size: 1rem;
  }

  .hero-description {
    font-size: 1rem;
  }

  .hero-buttons {
    flex-direction: column;
    width: 100%;
  }

  .btn {
    width: 100%;
    text-align: center;
  }

  .hero-meta {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.5rem;
  }

  .separator {
    display: none;
  }

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

  .publication-card {
    flex-direction: column;
    gap: 1rem;
  }

  .pub-year {
    width: auto;
  }

  .timeline::before {
    left: 7px;
  }

  .timeline-item {
    padding-left: 2.5rem;
  }

  .timeline-marker {
    left: 0;
  }

  .timeline-header {
    flex-direction: column;
  }

  .timeline-meta {
    text-align: left;
  }

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

  .education-card {
    flex-direction: column;
    gap: 1rem;
  }

  .edu-year {
    width: auto;
  }

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

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

@media (max-width: 480px) {
  .name {
    font-size: 2rem;
  }

  .hero-subtitle {
    font-size: 1.25rem;
  }

  .section-title {
    font-size: 1.75rem;
  }

  .pub-title {
    font-size: 1.125rem;
  }

  .timeline-title {
    font-size: 1.125rem;
  }

  .edu-degree {
    font-size: 1.125rem;
  }
}

/* ===========================
   Animations
   =========================== */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.fade-in-up {
  animation: fadeInUp 0.6s ease-out;
}

/* ===========================
   Utility Classes
   =========================== */
.text-center {
  text-align: center;
}

.mt-1 {
  margin-top: 0.5rem;
}

.mt-2 {
  margin-top: 1rem;
}

.mt-3 {
  margin-top: 1.5rem;
}

.mb-1 {
  margin-bottom: 0.5rem;
}

.mb-2 {
  margin-bottom: 1rem;
}

.mb-3 {
  margin-bottom: 1.5rem;
}