/* ===================================
   Custom Properties (CSS Variables)
   =================================== */

:root {
  /* Colors - Academic palette with deep blues and warm accents */
  --color-primary: #1a365d;
  --color-primary-light: #2c5282;
  --color-primary-dark: #0f2340;
  --color-accent: #d97706;
  --color-accent-light: #f59e0b;
  --color-text: #1a202c;
  --color-text-light: #4a5568;
  --color-bg: #ffffff;
  --color-bg-alt: #f7fafc;
  --color-bg-secondary: #edf2f7;
  --color-border: #cbd5e0;
  
  /* Typography */
  --font-display: 'Crimson Text', Georgia, serif;
  --font-body: 'Work Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  
  /* Spacing */
  --spacing-xs: 0.5rem;
  --spacing-sm: 1rem;
  --spacing-md: 2rem;
  --spacing-lg: 4rem;
  --spacing-xl: 6rem;
  
  /* Border radius */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  
  /* Shadows */
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.08), 0 1px 2px rgba(0, 0, 0, 0.06);
  --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.07), 0 2px 4px rgba(0, 0, 0, 0.06);
  --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1), 0 4px 6px rgba(0, 0, 0, 0.05);
  --shadow-xl: 0 20px 25px rgba(0, 0, 0, 0.1), 0 10px 10px rgba(0, 0, 0, 0.04);
  
  /* Transitions */
  --transition-base: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: all 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ===================================
   Base Styles & Reset
   =================================== */

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

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: var(--font-body);
  font-weight: 400;
  font-size: 1rem;
  line-height: 1.7;
  color: var(--color-text);
  background-color: var(--color-bg);
  overflow-x: hidden;
}

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-display);
  font-weight: 700;
  line-height: 1.3;
  color: var(--color-primary-dark);
}

h1 {
  font-size: clamp(2.5rem, 5vw, 4rem);
  letter-spacing: -0.02em;
}

h2 {
  font-size: clamp(2rem, 4vw, 3rem);
  margin-bottom: var(--spacing-lg);
  position: relative;
  display: inline-block;
}

h2::after {
  content: '';
  position: absolute;
  bottom: -0.5rem;
  left: 0;
  width: 60px;
  height: 4px;
  background: linear-gradient(90deg, var(--color-accent), var(--color-accent-light));
  border-radius: 2px;
}

h3 {
  font-size: clamp(1.5rem, 3vw, 2rem);
  margin-bottom: var(--spacing-sm);
}

p {
  margin-bottom: var(--spacing-sm);
}

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

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

ul {
  list-style: none;
}

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

/* ===================================
   Layout & Grid
   =================================== */

.row {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--spacing-md);
}

section {
  padding: var(--spacing-xl) 0;
  position: relative;
}

section:nth-child(even) {
  background-color: var(--color-bg-alt);
}

/* ===================================
   Header & Navigation
   =================================== */

.header {
  background: linear-gradient(135deg, var(--color-primary-dark) 0%, var(--color-primary) 100%);
  height: 100vh;
  min-height: 600px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  position: relative;
  color: white;
  overflow: hidden;
}

.header::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-image: 
    radial-gradient(circle at 20% 50%, rgba(255, 255, 255, 0.05) 0%, transparent 50%),
    radial-gradient(circle at 80% 80%, rgba(217, 119, 6, 0.1) 0%, transparent 50%);
  pointer-events: none;
}

.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);
  padding: var(--spacing-sm) 0;
  transition: var(--transition-base);
  opacity: 0;
  animation: fadeInDown 0.6s ease forwards 0.3s;
}

@keyframes fadeInDown {
  from {
    opacity: 0;
    transform: translateY(-20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.nav__items {
  display: flex;
  justify-content: flex-end;
  gap: var(--spacing-md);
  flex-wrap: wrap;
}

.nav__link {
  color: var(--color-text);
  font-weight: 500;
  font-size: 0.95rem;
  padding: var(--spacing-xs) var(--spacing-sm);
  border-radius: var(--radius-sm);
  transition: var(--transition-base);
  position: relative;
}

.nav__link::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 0;
  height: 2px;
  background: var(--color-accent);
  transition: var(--transition-base);
}

.nav__link:hover {
  color: var(--color-accent);
}

.nav__link:hover::after {
  width: 80%;
}

.header__text-box {
  text-align: center;
  z-index: 1;
  padding: var(--spacing-lg) var(--spacing-md);
  animation: fadeInUp 0.8s ease forwards;
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(30px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.heading-primary {
  color: white;
  margin-bottom: var(--spacing-sm);
  text-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
}

.header__subtitle {
  font-family: var(--font-display);
  font-size: clamp(1.25rem, 2.5vw, 1.75rem);
  font-weight: 600;
  color: var(--color-accent-light);
  margin-bottom: var(--spacing-sm);
  font-style: italic;
}

.header__description {
  font-size: clamp(1rem, 2vw, 1.25rem);
  color: rgba(255, 255, 255, 0.9);
  margin-bottom: var(--spacing-lg);
  max-width: 700px;
  margin-left: auto;
  margin-right: auto;
}

/* ===================================
   Buttons
   =================================== */

.btn {
  display: inline-block;
  padding: 1rem 2.5rem;
  font-family: var(--font-body);
  font-size: 1rem;
  font-weight: 600;
  text-align: center;
  border: none;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: var(--transition-base);
  text-decoration: none;
  position: relative;
  overflow: hidden;
}

.btn::before {
  content: '';
  position: absolute;
  top: 50%;
  left: 50%;
  width: 0;
  height: 0;
  border-radius: 50%;
  background: rgba(255, 255, 255, 0.3);
  transform: translate(-50%, -50%);
  transition: width 0.6s, height 0.6s;
}

.btn:hover::before {
  width: 300px;
  height: 300px;
}

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

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

/* ===================================
   About Section
   =================================== */

.about__content {
  display: grid;
  gap: var(--spacing-lg);
}

.about__text {
  font-size: 1.1rem;
  line-height: 1.8;
}

.about__text p:last-child {
  margin-top: var(--spacing-md);
  font-weight: 500;
  color: var(--color-primary);
}

.about__info {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--spacing-md);
  margin-top: var(--spacing-lg);
}

.about__info-item {
  background: white;
  padding: var(--spacing-md);
  border-radius: var(--radius-lg);
  border: 2px solid var(--color-border);
  transition: var(--transition-base);
}

.about__info-item:hover {
  border-color: var(--color-accent);
  box-shadow: var(--shadow-md);
  transform: translateY(-4px);
}

.about__info-item h3 {
  color: var(--color-primary);
  font-size: 1.5rem;
  margin-bottom: var(--spacing-sm);
  border-bottom: 2px solid var(--color-accent);
  padding-bottom: var(--spacing-xs);
}

.about__info-item p {
  margin-bottom: var(--spacing-xs);
  line-height: 1.6;
}

/* ===================================
   Research Section
   =================================== */

.research {
  background: var(--color-bg-secondary);
}

.research__grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--spacing-md);
}

.research__box {
  background: white;
  padding: var(--spacing-md);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  transition: var(--transition-base);
  border-left: 4px solid var(--color-accent);
}

.research__box:hover {
  transform: translateY(-6px);
  box-shadow: var(--shadow-lg);
}

.research__box h3 {
  color: var(--color-primary);
  margin-bottom: var(--spacing-sm);
  font-size: 1.5rem;
}

.research__box p {
  color: var(--color-text-light);
  margin-bottom: var(--spacing-md);
  line-height: 1.6;
}

.research__keywords {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-xs);
}

.research__keywords li {
  background: var(--color-bg-alt);
  padding: var(--spacing-xs) var(--spacing-sm);
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  color: var(--color-primary);
  border: 1px solid var(--color-border);
  transition: var(--transition-base);
}

.research__keywords li:hover {
  background: var(--color-accent);
  color: white;
  border-color: var(--color-accent);
}

/* ===================================
   Publications Section
   =================================== */

.publication {
  background: white;
  padding: var(--spacing-md);
  margin-bottom: var(--spacing-md);
  border-radius: var(--radius-md);
  border-left: 4px solid var(--color-primary);
  box-shadow: var(--shadow-sm);
  transition: var(--transition-base);
}

.publication:hover {
  box-shadow: var(--shadow-md);
  transform: translateX(4px);
}

.publication__type {
  display: inline-block;
  background: var(--color-accent);
  color: white;
  padding: 0.25rem 0.75rem;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  font-weight: 600;
  margin-bottom: var(--spacing-sm);
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.publication__title {
  font-size: 1.25rem;
  color: var(--color-primary-dark);
  margin-bottom: var(--spacing-xs);
  line-height: 1.4;
}

.publication__authors {
  font-weight: 500;
  color: var(--color-text);
  margin-bottom: 0.25rem;
}

.publication__venue {
  color: var(--color-text-light);
  font-style: italic;
  margin-bottom: var(--spacing-sm);
}

.publication__link {
  display: inline-flex;
  align-items: center;
  color: var(--color-accent);
  font-weight: 600;
  margin-top: var(--spacing-xs);
  transition: var(--transition-base);
}

.publication__link:hover {
  color: var(--color-accent-light);
  transform: translateX(4px);
}

.publications__note {
  margin-top: var(--spacing-lg);
  padding: var(--spacing-md);
  background: var(--color-bg-alt);
  border-radius: var(--radius-md);
  border-left: 4px solid var(--color-accent);
}

.publications__note p {
  margin: 0;
  color: var(--color-text-light);
}

/* ===================================
   Teaching Section
   =================================== */

.teaching {
  background: var(--color-bg-alt);
}

.teaching__content {
  display: grid;
  gap: var(--spacing-lg);
}

.teaching__summary {
  background: white;
  padding: var(--spacing-md);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
}

.teaching__summary p {
  font-size: 1.05rem;
  line-height: 1.7;
  margin-bottom: var(--spacing-sm);
}

.teaching__total {
  margin-top: var(--spacing-md);
  padding: var(--spacing-sm);
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-light) 100%);
  color: white;
  border-radius: var(--radius-md);
  text-align: center;
}

.teaching__positions {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--spacing-md);
}

.teaching__position {
  background: white;
  padding: var(--spacing-md);
  border-radius: var(--radius-lg);
  border: 2px solid var(--color-border);
  transition: var(--transition-base);
}

.teaching__position:hover {
  border-color: var(--color-accent);
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
}

.teaching__period {
  color: var(--color-accent);
  font-weight: 600;
  margin-bottom: var(--spacing-xs);
}

.teaching__courses {
  background: white;
  padding: var(--spacing-md);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
}

.teaching__courses h3 {
  color: var(--color-primary);
  margin-bottom: var(--spacing-md);
  font-size: 1.75rem;
}

.course {
  margin-bottom: var(--spacing-md);
  padding-bottom: var(--spacing-md);
  border-bottom: 1px solid var(--color-border);
}

.course:last-child {
  border-bottom: none;
  margin-bottom: 0;
  padding-bottom: 0;
}

.course h4 {
  color: var(--color-primary);
  font-size: 1.25rem;
  margin-bottom: var(--spacing-sm);
  font-family: var(--font-body);
  font-weight: 600;
}

.course ul {
  list-style: none;
  padding-left: 0;
}

.course li {
  padding: var(--spacing-xs) 0;
  padding-left: 1.5rem;
  position: relative;
  line-height: 1.6;
}

.course li::before {
  content: '▸';
  position: absolute;
  left: 0;
  color: var(--color-accent);
  font-weight: bold;
}

/* ===================================
   Skills Section
   =================================== */

.skills {
  background: linear-gradient(135deg, var(--color-primary-dark) 0%, var(--color-primary) 100%);
  color: white;
}

.skills h2 {
  color: white;
}

.skills h2::after {
  background: var(--color-accent-light);
}

.skills__grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--spacing-md);
}

.skills__category {
  background: rgba(255, 255, 255, 0.1);
  backdrop-filter: blur(10px);
  padding: var(--spacing-md);
  border-radius: var(--radius-lg);
  border: 1px solid rgba(255, 255, 255, 0.2);
  transition: var(--transition-base);
}

.skills__category:hover {
  background: rgba(255, 255, 255, 0.15);
  transform: translateY(-4px);
}

.skills__category h3 {
  color: var(--color-accent-light);
  margin-bottom: var(--spacing-md);
  font-size: 1.5rem;
}

.skills__category ul {
  list-style: none;
}

.skills__category li {
  padding: var(--spacing-xs) 0;
  padding-left: 1.5rem;
  position: relative;
  color: rgba(255, 255, 255, 0.9);
  line-height: 1.6;
}

.skills__category li::before {
  content: '✓';
  position: absolute;
  left: 0;
  color: var(--color-accent-light);
  font-weight: bold;
}

/* ===================================
   Contact Section
   =================================== */

.contact {
  background: var(--color-bg-secondary);
}

.contact__info {
  max-width: 800px;
  margin: 0 auto;
}

.contact__info > p {
  font-size: 1.1rem;
  text-align: center;
  margin-bottom: var(--spacing-lg);
  color: var(--color-text-light);
  line-height: 1.8;
}

.contact__details {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: var(--spacing-md);
  margin-top: var(--spacing-lg);
}

.contact__item {
  background: white;
  padding: var(--spacing-md);
  border-radius: var(--radius-lg);
  text-align: center;
  box-shadow: var(--shadow-sm);
  transition: var(--transition-base);
}

.contact__item:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
}

.contact__label {
  display: block;
  font-weight: 600;
  color: var(--color-primary);
  margin-bottom: var(--spacing-sm);
  font-size: 0.9rem;
  text-transform: uppercase;
  letter-spacing: 1px;
}

.contact__item p {
  margin: 0;
  color: var(--color-text);
  line-height: 1.6;
}

.contact__item .btn {
  margin-top: var(--spacing-xs);
}

/* ===================================
   Footer
   =================================== */

.footer {
  background: var(--color-primary-dark);
  color: rgba(255, 255, 255, 0.8);
  padding: var(--spacing-lg) 0;
  text-align: center;
}

.footer p {
  margin: 0;
  font-size: 0.95rem;
}

/* ===================================
   Back to Top Button
   =================================== */

.back-to-top {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  width: 50px;
  height: 50px;
  background: var(--color-accent);
  color: white;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow-lg);
  opacity: 0;
  visibility: hidden;
  transition: var(--transition-base);
  z-index: 999;
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
}

.back-to-top:hover {
  background: var(--color-accent-light);
  transform: translateY(-4px);
}

/* ===================================
   Responsive Design
   =================================== */

@media (max-width: 768px) {
  :root {
    --spacing-lg: 3rem;
    --spacing-xl: 4rem;
  }
  
  .nav__items {
    justify-content: center;
    gap: var(--spacing-sm);
  }
  
  .nav__link {
    font-size: 0.9rem;
    padding: var(--spacing-xs);
  }
  
  .header {
    height: auto;
    min-height: 100vh;
    padding: var(--spacing-lg) 0;
  }
  
  section {
    padding: var(--spacing-lg) 0;
  }
  
  .research__grid,
  .skills__grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .row {
    padding: 0 var(--spacing-sm);
  }
  
  .btn {
    padding: 0.85rem 2rem;
    font-size: 0.95rem;
  }
  
  .back-to-top {
    width: 45px;
    height: 45px;
    bottom: 1.5rem;
    right: 1.5rem;
  }
}

/* ===================================
   Animations & Effects
   =================================== */

@keyframes fadeIn {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}

@keyframes slideInLeft {
  from {
    opacity: 0;
    transform: translateX(-30px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes slideInRight {
  from {
    opacity: 0;
    transform: translateX(30px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

/* Smooth scroll snap for sections (optional) */
@media (min-width: 1024px) {
  html {
    scroll-snap-type: y proximity;
  }
  
  section {
    scroll-snap-align: start;
  }
}

/* Print styles */
@media print {
  .nav,
  .back-to-top {
    display: none;
  }
  
  section {
    page-break-inside: avoid;
  }
}