/* ===== CSS RESET & BASE STYLES ===== */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

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

body {
  font-family: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    sans-serif;
  line-height: 1.6;
  color: var(--text-primary);
  background-color: var(--bg-primary);
  overflow-x: hidden;
}

/* ===== TYPOGRAPHY ===== */
h1,
h2,
h3,
h4,
h5,
h6 {
  font-family: "Caveat", cursive;
  font-weight: 600;
  line-height: 1.2;
  margin-bottom: 1rem;
  color: var(--text-primary);
}

h1 {
  font-size: 2rem;
}
h2 {
  font-size: 1.75rem;
}
h3 {
  font-size: 1.5rem;
}
h4 {
  font-size: 1.25rem;
}
h5 {
  font-size: 1.125rem;
}
h6 {
  font-size: 1rem;
}

p {
  margin-bottom: 1rem;
  font-size: 1rem;
  line-height: 1.8;
}

a {
  color: var(--text-primary);
  text-decoration: none;
  transition: all 0.3s ease;
}

a:hover {
  color: var(--text-accent);
  transform: translateY(-1px);
}

/* Math equations */
.math {
  font-family: "Charter", Georgia, serif;
}

/* Code blocks */
code,
pre {
  font-family: "Fira Code", "Courier New", monospace;
}

pre {
  background-color: #2d3748;
  color: #e2e8f0;
  padding: 1.5rem;
  border-radius: 8px;
  overflow-x: auto;
  margin: 1rem 0;
}

code {
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
  padding: 0.2rem 0.4rem;
  border-radius: 4px;
  font-size: 0.9em;
}

/* ===== LAYOUT SYSTEM ===== */
.container-main {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 2rem;
  width: 80%;
}

.container-large {
  max-width: 1400px;
  margin: 0 auto;
  padding: 0 2rem;
  width: 90%;
}

.container-max {
  max-width: 100%;
  margin: 0 auto;
  padding: 0;
  width: 100%;
}

/* Grid System */
.grid-columns-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 2rem;
}

.grid-columns-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 2rem;
}

.grid-columns-4 {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 2rem;
}

/* ===== HEADER & NAVIGATION ===== */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  background-color: rgba(248, 249, 250, 0.95);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border-color);
  z-index: 1000;
  transition: all 0.3s ease;
}

.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1rem 2rem;
  max-width: 1200px;
  margin: 0 auto;
}

.nav-brand {
  flex: 1;
}

.nav-logo {
  font-family: "Caveat", cursive;
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--text-primary);
  transition: all 0.3s ease;
}

.nav-logo:hover {
  color: var(--text-accent);
  transform: none;
}

.nav-menu {
  display: flex;
  align-items: center;
  gap: 2rem;
  flex: 2;
  justify-content: center;
}

.nav-link {
  font-weight: 500;
  padding: 0.5rem 1rem;
  border-radius: 6px;
  transition: all 0.3s ease;
  position: relative;
  color: var(--text-secondary);
}

.nav-link:hover,
.nav-link.active {
  color: var(--text-accent);
  background-color: rgba(253, 126, 20, 0.1);
}

.nav-social {
  display: flex;
  align-items: center;
  gap: 1rem;
  flex: 1;
  justify-content: flex-end;
}

.social-link {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background-color: var(--bg-tertiary);
  color: var(--text-secondary);
  transition: all 0.3s ease;
}

.social-link:hover {
  background-color: var(--text-accent);
  color: white;
  transform: translateY(-2px);
}

.nav-toggle {
  display: none;
  flex-direction: column;
  cursor: pointer;
  padding: 0.5rem;
}

.hamburger {
  width: 25px;
  height: 3px;
  background-color: #495057;
  margin: 3px 0;
  transition: 0.3s;
  border-radius: 2px;
}

/* ===== MAIN CONTENT ===== */
.main {
  margin-top: 80px;
  min-height: calc(100vh - 80px);
}

/* ===== HERO SECTION ===== */
.hero {
  padding: 4rem 0;
  background: linear-gradient(
    135deg,
    var(--bg-primary) 0%,
    var(--bg-tertiary) 100%
  );
  text-align: center;
}

.hero-title {
  font-size: 3.5rem;
  font-weight: 700;
  margin-bottom: 1rem;
  color: var(--text-primary);
}

.hero-subtitle {
  font-size: 1.5rem;
  color: var(--text-secondary);
  margin-bottom: 2rem;
  font-weight: 400;
}

.hero-bio {
  font-size: 1.1rem;
  margin: 0 auto 2rem;
  color: var(--text-primary);
  line-height: 1.8;
}

/* ===== BUTTONS ===== */
.btn {
  display: inline-block;
  padding: 0.75rem 2rem;
  border-radius: 6px;
  font-weight: 500;
  text-align: center;
  transition: all 0.3s ease;
  cursor: pointer;
  border: 2px solid transparent;
  text-decoration: none;
  font-size: 1rem;
}

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

.btn-primary:hover {
  background-color: #e76f00;
  border-color: #e76f00;
  color: white;
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(253, 126, 20, 0.3);
}

.btn-outline {
  background-color: transparent;
  color: var(--text-primary);
  border-color: var(--text-primary);
}

.btn-outline:hover {
  background-color: var(--text-primary);
  color: var(--bg-primary);
  transform: translateY(-2px);
}

/* ===== SECTIONS ===== */
.section-title {
  text-align: center;
  margin-bottom: 3rem;
  position: relative;
  color: var(--text-primary);
}

.section-title::after {
  content: "";
  position: absolute;
  bottom: -10px;
  left: 50%;
  transform: translateX(-50%);
  width: 60px;
  height: 3px;
  background-color: var(--text-accent);
  border-radius: 2px;
}

/* ===== FEATURED PROJECTS ===== */
.featured-projects {
  padding: 4rem 0;
  background-color: var(--bg-secondary);
}

.project-card {
  background-color: var(--bg-primary);
  border-radius: 12px;
  padding: 2rem;
  transition: all 0.3s ease;
  border: 1px solid var(--border-color);
  height: 100%;
  display: flex;
  flex-direction: column;
  position: relative;
}

.project-card:hover {
  transform: translateY(-5px);
  box-shadow: var(--shadow);
  border-color: var(--text-accent);
}

.project-status {
  position: absolute;
  top: 1rem;
  right: 1rem;
  padding: 0.25rem 0.75rem;
  border-radius: 20px;
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.project-status.in-progress {
  background-color: #fff3cd;
  color: #856404;
  border: 1px solid #ffeaa7;
}

.project-detail .project-status {
  position: static;
  display: inline-block;
  margin-bottom: 1rem;
}

.project-thumbnail {
  width: 100%;
  height: 200px;
  object-fit: cover;
  border-radius: 8px;
  margin-bottom: 1rem;
}

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

.project-description {
  color: var(--text-secondary);
  margin-bottom: 1rem;
  flex-grow: 1;
}

.project-link {
  color: var(--text-accent);
  font-weight: 500;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
}

.project-link:hover {
  transform: none;
}

/* ===== PUBLICATIONS ===== */
.publications-section {
  padding: 4rem 0;
  background-color: var(--bg-primary);
}

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

.publication-item {
  background-color: var(--bg-secondary);
  border-radius: 12px;
  padding: 2rem;
  margin-bottom: 2rem;
  border: 1px solid var(--border-color);
  transition: all 0.3s ease;
}

.publication-item:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow);
}

.publication-title {
  font-size: 1.3rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.publication-title a {
  color: inherit;
  text-decoration: none;
}

.publication-title a:hover {
  color: var(--text-accent);
}

.publication-authors {
  color: var(--text-secondary);
  margin-bottom: 0.5rem;
  font-style: italic;
}

.publication-venue {
  color: var(--text-accent);
  font-weight: 500;
  margin-bottom: 1rem;
}

.publication-abstract,
.publication-description {
  color: var(--text-primary);
  line-height: 1.7;
  margin-bottom: 1rem;
}

.status-badge {
  display: inline-block;
  padding: 0.25rem 0.75rem;
  border-radius: 20px;
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-left: 1rem;
}

.status-badge.under-review {
  background-color: #fff3cd;
  color: #856404;
  border: 1px solid #ffeaa7;
}

.status-badge.published {
  background-color: #d4edda;
  color: #155724;
  border: 1px solid #c3e6cb;
}

.publication-title {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.publication-keywords {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.keyword-tag {
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
  padding: 0.25rem 0.75rem;
  border-radius: 20px;
  font-size: 0.85rem;
  font-weight: 500;
}

/* ===== ABOUT PAGE ===== */
.about-hero {
  padding: 4rem 0;
  background-color: white;
}

.about-intro {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 3rem;
  align-items: center;
}

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

.profile-img {
  width: 200px;
  height: 200px;
  border-radius: 50%;
  object-fit: cover;
  border: 4px solid #e9ecef;
  transition: all 0.3s ease;
  filter: grayscale(100%);
}

.profile-img:hover {
  filter: grayscale(0%);
  transform: scale(1.05);
}

.page-title {
  font-size: 3rem;
  margin-bottom: 1rem;
  color: #212529;
}

.page-subtitle {
  font-size: 1.25rem;
  color: #6c757d;
  margin-bottom: 2rem;
}

.about-description {
  font-size: 1.1rem;
  line-height: 1.8;
  margin-bottom: 1.5rem;
  color: #495057;
}

/* ===== TIMELINE ===== */
.timeline-section {
  padding: 4rem 0;
  background-color: #f8f9fa;
}

.timeline {
  position: relative;
  max-width: 800px;
  margin: 0 auto;
}

.timeline::before {
  content: "";
  position: absolute;
  left: 50%;
  top: 0;
  bottom: 0;
  width: 2px;
  background-color: #e9ecef;
  transform: translateX(-50%);
}

.timeline-item {
  display: flex;
  margin-bottom: 3rem;
  position: relative;
}

.timeline-item:nth-child(odd) {
  flex-direction: row;
}

.timeline-item:nth-child(even) {
  flex-direction: row-reverse;
}

.timeline-date {
  flex: 0 0 200px;
  text-align: center;
  font-weight: 600;
  color: #fd7e14;
  padding: 1rem;
  background-color: white;
  border-radius: 8px;
  margin: 0 2rem;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
}

.timeline-content {
  flex: 1;
  background-color: white;
  padding: 2rem;
  border-radius: 12px;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
  border: 1px solid #e9ecef;
}

.timeline-content h3 {
  color: #212529;
  margin-bottom: 0.5rem;
}

.timeline-location {
  color: #fd7e14;
  font-weight: 500;
  margin-bottom: 1rem;
}

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

.timeline-details li {
  padding: 0.25rem 0;
  color: #495057;
  position: relative;
  padding-left: 1.5rem;
}

.timeline-details li::before {
  content: "•";
  color: #fd7e14;
  font-weight: bold;
  position: absolute;
  left: 0;
}

/* ===== SKILLS ===== */
.skills-section {
  padding: 4rem 0;
  background-color: white;
}

.skills-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 2rem;
}

.skill-category h3 {
  color: #212529;
  margin-bottom: 1rem;
  font-size: 1.25rem;
}

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

.skill-tag {
  background-color: #495057;
  color: white;
  padding: 0.5rem 1rem;
  border-radius: 20px;
  font-size: 0.9rem;
  font-weight: 500;
  transition: all 0.3s ease;
}

.skill-tag:hover {
  background-color: #fd7e14;
  transform: translateY(-2px);
}

/* ===== CONTACT ===== */
.contact-section {
  padding: 4rem 0;
  background-color: #f8f9fa;
}

.contact-content {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 4rem;
  align-items: start;
}

.contact-text {
  font-size: 1.1rem;
  line-height: 1.8;
  margin-bottom: 2rem;
  color: #495057;
}

.contact-methods {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.contact-method {
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 1rem;
  background-color: white;
  border-radius: 8px;
  border: 1px solid #e9ecef;
  transition: all 0.3s ease;
}

.contact-method:hover {
  transform: translateX(5px);
  border-color: #fd7e14;
}

.contact-method i {
  color: #fd7e14;
  font-size: 1.2rem;
  width: 20px;
}

/* ===== FORMS ===== */
.contact-form {
  background-color: white;
  padding: 2rem;
  border-radius: 12px;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
  border: 1px solid #e9ecef;
}

.form-group {
  margin-bottom: 1.5rem;
}

.form-label {
  display: block;
  margin-bottom: 0.5rem;
  font-weight: 500;
  color: #212529;
}

.form-input,
.form-textarea {
  width: 100%;
  padding: 0.75rem;
  border: 2px solid #e9ecef;
  border-radius: 6px;
  font-size: 1rem;
  transition: all 0.3s ease;
  font-family: inherit;
}

.form-input:focus,
.form-textarea:focus {
  outline: none;
  border-color: #fd7e14;
  box-shadow: 0 0 0 3px rgba(253, 126, 20, 0.1);
}

.form-textarea {
  resize: vertical;
  min-height: 120px;
}

/* ===== PROJECTS PAGE ===== */
.projects-hero {
  padding: 4rem 0;
  background: linear-gradient(135deg, #f8f9fa 0%, #e9ecef 100%);
  text-align: center;
}

/* ===== LIBRARY PAGE ===== */
.library-hero {
  padding: 4rem 0;
  background: linear-gradient(135deg, #f8f9fa 0%, #e9ecef 100%);
  text-align: center;
}

.library-section {
  padding: 4rem 0;
  background-color: white;
}

.library-section:nth-child(even) {
  background-color: #f8f9fa;
}

.books-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
  gap: 2rem;
  margin-top: 2rem;
}

.book-card {
  background: white;
  border-radius: 12px;
  padding: 2rem;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
  transition: all 0.3s ease;
  border: 1px solid #e9ecef;
  display: flex;
  gap: 1.5rem;
  align-items: flex-start;
}

.book-card:hover {
  transform: translateY(-5px);
  box-shadow: 0 8px 25px rgba(0, 0, 0, 0.15);
  border-color: #667eea;
}

.book-cover {
  width: 60px;
  height: 80px;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-size: 1.5rem;
  flex-shrink: 0;
}

.book-info {
  flex: 1;
}

.book-title {
  font-size: 1.25rem;
  font-weight: 600;
  color: #2c3e50;
  margin-bottom: 0.5rem;
  line-height: 1.3;
}

.book-author {
  color: #667eea;
  font-weight: 500;
  margin-bottom: 0.75rem;
  font-size: 0.95rem;
}

.book-description {
  color: #6c757d;
  line-height: 1.6;
  font-size: 0.9rem;
}

.projects-section {
  padding: 4rem 0;
  background-color: white;
}

.projects-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(400px, 1fr));
  gap: 3rem;
  margin-top: 2rem;
}

.project-detail {
  background-color: #f8f9fa;
  border-radius: 12px;
  padding: 3rem;
  border: 1px solid #e9ecef;
  transition: all 0.3s ease;
  margin-bottom: 2rem;
}

.project-detail:hover {
  transform: translateY(-5px);
  box-shadow: 0 8px 25px rgba(0, 0, 0, 0.1);
}

.project-thumbnail {
  width: 100%;
  height: 200px;
  object-fit: cover;
  border-radius: 8px;
  margin-bottom: 1rem;
}

.tech-stack {
  margin: 2rem 0 1.5rem 0;
}

.tech-stack h4 {
  margin-bottom: 0.5rem;
  color: #495057;
  font-size: 1rem;
}

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

.tech-tag {
  background: #f8f9fa;
  color: #495057;
  padding: 0.25rem 0.75rem;
  border-radius: 20px;
  font-size: 0.875rem;
  border: 1px solid #dee2e6;
  transition: all 0.3s ease;
}

.tech-tag:hover {
  background: #667eea;
  color: white;
  border-color: #667eea;
}

.equation {
  margin: 1rem 0;
  padding: 1rem;
  background: #f8f9fa;
  border-radius: 8px;
  border-left: 4px solid #667eea;
  font-family: "Charter", serif;
}

.project-detail h3 {
  color: #212529;
  margin-bottom: 1rem;
}

.project-detail p {
  color: #495057;
  margin-bottom: 1.5rem;
}

.tech-stack {
  background-color: #2d3748;
  color: #e2e8f0;
  padding: 1rem;
  border-radius: 6px;
  font-family: "Fira Code", monospace;
  font-size: 0.9rem;
  margin-bottom: 1rem;
  overflow-x: auto;
}

.results-table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 2rem;
  background-color: white;
  border-radius: 8px;
  overflow: hidden;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
}

.results-table th,
.results-table td {
  padding: 0.75rem;
  text-align: left;
  border-bottom: 1px solid #e9ecef;
}

.results-table th {
  background-color: #495057;
  color: white;
  font-weight: 600;
}

.results-table tr:nth-child(even) {
  background-color: #f8f9fa;
}

.results-table tr:hover {
  background-color: #e9ecef;
}

/* ===== INTERACTIVE DEMOS ===== */
.demos-section {
  padding: 4rem 0;
  background-color: #f8f9fa;
}

.demo-container {
  background-color: white;
  border-radius: 12px;
  padding: 2rem;
  margin-bottom: 3rem;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
  border: 1px solid #e9ecef;
}

.demo-title {
  color: #212529;
  margin-bottom: 0.5rem;
  font-size: 1.5rem;
}

.demo-description {
  color: #6c757d;
  margin-bottom: 2rem;
}

/* Image Comparison Slider */
.image-comparison {
  position: relative;
  max-width: 600px;
  margin: 0 auto;
}

.comparison-container {
  position: relative;
  border-radius: 8px;
  overflow: hidden;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
}

.comparison-image {
  width: 100%;
  height: 400px;
  object-fit: cover;
  display: block;
}

.comparison-after {
  position: absolute;
  top: 0;
  left: 0;
  clip-path: polygon(50% 0%, 100% 0%, 100% 100%, 50% 100%);
}

.comparison-slider {
  position: absolute;
  top: 0;
  left: 50%;
  width: 4px;
  height: 100%;
  background-color: #fd7e14;
  cursor: ew-resize;
  transform: translateX(-50%);
}

.comparison-handle {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 40px;
  height: 40px;
  background-color: #fd7e14;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-size: 1.2rem;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.3);
}

.comparison-labels {
  display: flex;
  justify-content: space-between;
  margin-top: 1rem;
  font-weight: 500;
  color: #495057;
}

/* Video Demo */
.video-demo {
  text-align: center;
}

.demo-video {
  width: 100%;
  max-width: 800px;
  border-radius: 8px;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
}

.video-controls {
  display: flex;
  justify-content: center;
  gap: 1rem;
  margin-top: 1rem;
}

.video-btn {
  padding: 0.5rem 1rem;
  border: 2px solid #e9ecef;
  background-color: white;
  color: #495057;
  border-radius: 6px;
  cursor: pointer;
  transition: all 0.3s ease;
  font-weight: 500;
}

.video-btn:hover,
.video-btn.active {
  border-color: #fd7e14;
  background-color: #fd7e14;
  color: white;
}

/* Model Selection Demo */
.model-demo {
  display: grid;
  grid-template-columns: 200px 1fr;
  gap: 2rem;
  align-items: start;
}

.model-selector {
  position: sticky;
  top: 100px;
}

.model-select {
  width: 100%;
  padding: 0.75rem;
  border: 2px solid #e9ecef;
  border-radius: 6px;
  background-color: white;
  font-size: 1rem;
  cursor: pointer;
  transition: all 0.3s ease;
}

.model-select:focus {
  outline: none;
  border-color: #fd7e14;
}

.model-output {
  text-align: center;
}

.model-image {
  width: 100%;
  max-width: 400px;
  height: 300px;
  object-fit: cover;
  border-radius: 8px;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
  margin-bottom: 1rem;
}

.model-stats {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1rem;
  max-width: 400px;
  margin: 0 auto;
}

.stat-item {
  background-color: #f8f9fa;
  padding: 1rem;
  border-radius: 8px;
  border: 1px solid #e9ecef;
}

.stat-label {
  display: block;
  font-size: 0.9rem;
  color: #6c757d;
  margin-bottom: 0.25rem;
}

.stat-value {
  display: block;
  font-size: 1.2rem;
  font-weight: 600;
  color: #212529;
}

/* ===== FOOTER ===== */
.footer {
  background-color: var(--text-primary);
  color: var(--bg-primary);
  padding: 2rem 0;
  margin-top: 4rem;
}

.footer-content {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
}

.footer-link {
  color: var(--text-secondary);
  transition: all 0.3s ease;
}

.footer-link:hover {
  color: var(--text-accent);
}

.back-to-top {
  background-color: var(--text-accent);
  color: white;
  border: none;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.3s ease;
}

.back-to-top:hover {
  background-color: #e76f00;
  transform: translateY(-2px);
}

/* ===== DARK MODE TOGGLE ===== */
.theme-toggle {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  width: 60px;
  height: 60px;
  border-radius: 50%;
  border: none;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  color: white;
  font-size: 1.5rem;
  cursor: pointer;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
  transition: all 0.3s ease;
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: center;
}

.theme-toggle:hover {
  transform: scale(1.1);
  box-shadow: 0 6px 20px rgba(0, 0, 0, 0.3);
}

.theme-toggle.dark {
  background: linear-gradient(135deg, #2c3e50 0%, #34495e 100%);
}

/* ===== THEME VARIABLES ===== */
:root {
  --bg-primary: #f8f9fa;
  --bg-secondary: #ffffff;
  --bg-tertiary: #e9ecef;
  --text-primary: #212529;
  --text-secondary: #6c757d;
  --text-accent: #fd7e14;
  --border-color: #e9ecef;
  --shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
}

/* ===== DARK MODE STYLES ===== */
[data-theme="dark"] {
  --bg-primary: #0f1419;
  --bg-secondary: #1a1f2e;
  --bg-tertiary: #2d3748;
  --text-primary: #e2e8f0;
  --text-secondary: #a0aec0;
  --text-accent: #9f7aea;
  --border-color: #4a5568;
  --shadow: 0 4px 15px rgba(0, 0, 0, 0.3);
}

[data-theme="dark"] body {
  background-color: var(--bg-primary);
  color: var(--text-primary);
}

[data-theme="dark"] .header {
  background-color: rgba(15, 20, 25, 0.95);
  border-bottom-color: var(--border-color);
}

[data-theme="dark"] .nav-logo {
  color: var(--text-primary);
}

[data-theme="dark"] .nav-link {
  color: var(--text-secondary);
}

[data-theme="dark"] .nav-link:hover,
[data-theme="dark"] .nav-link.active {
  color: var(--text-accent);
  background-color: rgba(159, 122, 234, 0.1);
}

[data-theme="dark"] .social-link {
  background-color: var(--bg-tertiary);
  color: var(--text-secondary);
}

[data-theme="dark"] .social-link:hover {
  background-color: var(--text-accent);
  color: white;
}

[data-theme="dark"] .hero {
  background: linear-gradient(
    135deg,
    var(--bg-primary) 0%,
    var(--bg-secondary) 100%
  );
}

[data-theme="dark"] .hero-title {
  color: var(--text-primary);
}

[data-theme="dark"] .hero-subtitle {
  color: var(--text-secondary);
}

[data-theme="dark"] .hero-bio {
  color: var(--text-primary);
}

[data-theme="dark"] .section-title {
  color: var(--text-primary);
}

[data-theme="dark"] .section-title::after {
  background-color: var(--text-accent);
}

[data-theme="dark"] .project-card {
  background-color: var(--bg-secondary);
  border-color: var(--border-color);
}

[data-theme="dark"] .project-card:hover {
  border-color: var(--text-accent);
  box-shadow: 0 8px 25px rgba(159, 122, 234, 0.2);
}

[data-theme="dark"] .project-status.in-progress {
  background-color: rgba(255, 193, 7, 0.2);
  color: #ffc107;
  border-color: rgba(255, 193, 7, 0.3);
}

[data-theme="dark"] .project-detail .project-status {
  background-color: rgba(255, 193, 7, 0.2);
  color: #ffc107;
  border-color: rgba(255, 193, 7, 0.3);
}

[data-theme="dark"] .project-title {
  color: var(--text-primary);
}

[data-theme="dark"] .project-description {
  color: var(--text-secondary);
}

[data-theme="dark"] .project-link {
  color: var(--text-accent);
}

[data-theme="dark"] .publication-item {
  background-color: var(--bg-secondary);
  border-color: var(--border-color);
}

[data-theme="dark"] .publication-item:hover {
  box-shadow: 0 4px 15px rgba(159, 122, 234, 0.2);
}

[data-theme="dark"] .publication-title {
  color: var(--text-primary);
}

[data-theme="dark"] .publication-title a {
  color: var(--text-primary);
}

[data-theme="dark"] .publication-title a:hover {
  color: var(--text-accent);
}

[data-theme="dark"] .publication-authors {
  color: var(--text-secondary);
}

[data-theme="dark"] .publication-venue {
  color: var(--text-accent);
}

[data-theme="dark"] .publication-abstract,
[data-theme="dark"] .publication-description {
  color: var(--text-primary);
}

[data-theme="dark"] .status-badge.under-review {
  background-color: rgba(255, 193, 7, 0.2);
  color: #ffc107;
  border-color: rgba(255, 193, 7, 0.3);
}

[data-theme="dark"] .status-badge.published {
  background-color: rgba(40, 167, 69, 0.2);
  color: #28a745;
  border-color: rgba(40, 167, 69, 0.3);
}

[data-theme="dark"] .keyword-tag {
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
}

[data-theme="dark"] .footer {
  background-color: var(--bg-secondary);
  color: var(--text-primary);
}

[data-theme="dark"] .footer-link {
  color: var(--text-secondary);
}

[data-theme="dark"] .footer-link:hover {
  color: var(--text-accent);
}

[data-theme="dark"] .back-to-top {
  background-color: var(--text-accent);
}

[data-theme="dark"] .back-to-top:hover {
  background-color: #805ad5;
}

/* ===== DARK MODE - ADDITIONAL SECTIONS ===== */
[data-theme="dark"] .featured-projects {
  background-color: var(--bg-primary);
}

[data-theme="dark"] .publications-section {
  background-color: var(--bg-secondary);
}

[data-theme="dark"] .about-hero {
  background-color: var(--bg-primary);
}

[data-theme="dark"] .page-title {
  color: var(--text-primary);
}

[data-theme="dark"] .page-subtitle {
  color: var(--text-secondary);
}

[data-theme="dark"] .about-description {
  color: var(--text-primary);
}

[data-theme="dark"] .timeline-section {
  background-color: var(--bg-secondary);
}

[data-theme="dark"] .timeline-content {
  background-color: var(--bg-primary);
  border-color: var(--border-color);
  box-shadow: 0 4px 15px rgba(159, 122, 234, 0.1);
}

[data-theme="dark"] .timeline-content h3 {
  color: var(--text-primary);
}

[data-theme="dark"] .timeline-location {
  color: var(--text-accent);
}

[data-theme="dark"] .timeline-details li {
  color: var(--text-primary);
}

[data-theme="dark"] .timeline-details li::before {
  color: var(--text-accent);
}

[data-theme="dark"] .timeline-date {
  background-color: var(--bg-primary);
  color: var(--text-accent);
  box-shadow: 0 2px 8px rgba(159, 122, 234, 0.2);
}

[data-theme="dark"] .skills-section {
  background-color: var(--bg-primary);
}

[data-theme="dark"] .skill-category h3 {
  color: var(--text-primary);
}

[data-theme="dark"] .skill-tag {
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
}

[data-theme="dark"] .skill-tag:hover {
  background-color: var(--text-accent);
  color: white;
}

[data-theme="dark"] .contact-section {
  background-color: var(--bg-secondary);
}

[data-theme="dark"] .contact-text {
  color: var(--text-primary);
}

[data-theme="dark"] .contact-method {
  background-color: var(--bg-primary);
  border-color: var(--border-color);
}

[data-theme="dark"] .contact-method:hover {
  border-color: var(--text-accent);
}

[data-theme="dark"] .contact-method i {
  color: var(--text-accent);
}

[data-theme="dark"] .projects-hero {
  background: linear-gradient(
    135deg,
    var(--bg-primary) 0%,
    var(--bg-secondary) 100%
  );
}

[data-theme="dark"] .projects-section {
  background-color: var(--bg-primary);
}

[data-theme="dark"] .project-detail {
  background-color: var(--bg-secondary);
  border-color: var(--border-color);
}

[data-theme="dark"] .project-detail:hover {
  box-shadow: 0 8px 25px rgba(159, 122, 234, 0.2);
}

[data-theme="dark"] .project-detail h3 {
  color: var(--text-primary);
}

[data-theme="dark"] .project-detail p {
  color: var(--text-primary);
}

[data-theme="dark"] .tech-stack {
  background-color: #1a202c;
  color: #e2e8f0;
}

[data-theme="dark"] .results-table {
  background-color: var(--bg-primary);
  box-shadow: 0 2px 8px rgba(159, 122, 234, 0.1);
}

[data-theme="dark"] .results-table th {
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
}

[data-theme="dark"] .results-table tr:nth-child(even) {
  background-color: var(--bg-secondary);
}

[data-theme="dark"] .results-table tr:hover {
  background-color: var(--bg-tertiary);
}

[data-theme="dark"] .results-table td {
  color: var(--text-primary);
  border-bottom-color: var(--border-color);
}

[data-theme="dark"] .demos-section {
  background-color: var(--bg-secondary);
}

[data-theme="dark"] .demo-container {
  background-color: var(--bg-primary);
  border-color: var(--border-color);
  box-shadow: 0 4px 15px rgba(159, 122, 234, 0.1);
}

[data-theme="dark"] .demo-title {
  color: var(--text-primary);
}

[data-theme="dark"] .demo-description {
  color: var(--text-secondary);
}

[data-theme="dark"] .comparison-container {
  box-shadow: 0 4px 15px rgba(159, 122, 234, 0.2);
}

[data-theme="dark"] .comparison-slider {
  background-color: var(--text-accent);
}

[data-theme="dark"] .comparison-handle {
  background-color: var(--text-accent);
  box-shadow: 0 2px 8px rgba(159, 122, 234, 0.4);
}

[data-theme="dark"] .comparison-labels {
  color: var(--text-primary);
}

[data-theme="dark"] .demo-video {
  box-shadow: 0 4px 15px rgba(159, 122, 234, 0.2);
}

[data-theme="dark"] .video-btn {
  background-color: var(--bg-primary);
  border-color: var(--border-color);
  color: var(--text-primary);
}

[data-theme="dark"] .video-btn:hover,
[data-theme="dark"] .video-btn.active {
  border-color: var(--text-accent);
  background-color: var(--text-accent);
  color: white;
}

[data-theme="dark"] .model-select {
  background-color: var(--bg-primary);
  border-color: var(--border-color);
  color: var(--text-primary);
}

[data-theme="dark"] .model-select:focus {
  border-color: var(--text-accent);
}

[data-theme="dark"] .model-image {
  box-shadow: 0 4px 15px rgba(159, 122, 234, 0.1);
}

[data-theme="dark"] .stat-item {
  background-color: var(--bg-secondary);
  border-color: var(--border-color);
}

[data-theme="dark"] .stat-label {
  color: var(--text-secondary);
}

[data-theme="dark"] .stat-value {
  color: var(--text-primary);
}

[data-theme="dark"] .btn-primary {
  background-color: var(--text-accent);
  border-color: var(--text-accent);
  color: white;
}

[data-theme="dark"] .btn-primary:hover {
  background-color: #805ad5;
  border-color: #805ad5;
  box-shadow: 0 4px 12px rgba(159, 122, 234, 0.4);
}

[data-theme="dark"] .btn-outline {
  background-color: transparent;
  color: var(--text-primary);
  border-color: var(--text-primary);
}

[data-theme="dark"] .btn-outline:hover {
  background-color: var(--text-primary);
  color: var(--bg-primary);
}

[data-theme="dark"] .form-input,
[data-theme="dark"] .form-textarea {
  background-color: var(--bg-primary);
  border-color: var(--border-color);
  color: var(--text-primary);
}

[data-theme="dark"] .form-input:focus,
[data-theme="dark"] .form-textarea:focus {
  border-color: var(--text-accent);
  box-shadow: 0 0 0 3px rgba(159, 122, 234, 0.1);
}

[data-theme="dark"] .form-label {
  color: var(--text-primary);
}

[data-theme="dark"] .hamburger {
  background-color: var(--text-primary);
}

[data-theme="dark"] .nav-menu {
  background-color: rgba(15, 20, 25, 0.98);
}

[data-theme="dark"] .profile-img {
  border-color: var(--border-color);
}

[data-theme="dark"] .profile-img:hover {
  border-color: var(--text-accent);
}

[data-theme="dark"] .timeline::before {
  background-color: var(--border-color);
}

[data-theme="dark"] h1,
[data-theme="dark"] h2,
[data-theme="dark"] h3,
[data-theme="dark"] h4,
[data-theme="dark"] h5,
[data-theme="dark"] h6 {
  color: var(--text-primary);
}

[data-theme="dark"] p {
  color: var(--text-primary);
}

[data-theme="dark"] a {
  color: var(--text-primary);
}

[data-theme="dark"] a:hover {
  color: var(--text-accent);
}

[data-theme="dark"] code {
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
}

[data-theme="dark"] pre {
  background-color: #1a202c;
  color: #e2e8f0;
}

[data-theme="dark"] .tech-stack h4 {
  color: var(--text-primary);
}

[data-theme="dark"] .tech-tag {
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
  border-color: var(--border-color);
}

[data-theme="dark"] .tech-tag:hover {
  background-color: var(--text-accent);
  color: white;
  border-color: var(--text-accent);
}

[data-theme="dark"] .equation {
  background-color: var(--bg-secondary);
  color: var(--text-primary);
  border-left-color: var(--text-accent);
}

[data-theme="dark"] .library-hero {
  background: linear-gradient(
    135deg,
    var(--bg-primary) 0%,
    var(--bg-secondary) 100%
  );
}

[data-theme="dark"] .library-section {
  background-color: var(--bg-primary);
}

[data-theme="dark"] .library-section:nth-child(even) {
  background-color: var(--bg-secondary);
}

[data-theme="dark"] .book-card {
  background-color: var(--bg-secondary);
  border-color: var(--border-color);
}

[data-theme="dark"] .book-card:hover {
  border-color: var(--text-accent);
  box-shadow: 0 8px 25px rgba(159, 122, 234, 0.2);
}

[data-theme="dark"] .book-title {
  color: var(--text-primary);
}

[data-theme="dark"] .book-author {
  color: var(--text-accent);
}

[data-theme="dark"] .book-description {
  color: var(--text-secondary);
}

/* ===== UTILITY CLASSES ===== */
.text-center {
  text-align: center;
}
.text-left {
  text-align: left;
}
.text-right {
  text-align: right;
}

.mb-1 {
  margin-bottom: 0.5rem;
}
.mb-2 {
  margin-bottom: 1rem;
}
.mb-3 {
  margin-bottom: 1.5rem;
}
.mb-4 {
  margin-bottom: 2rem;
}

.mt-1 {
  margin-top: 0.5rem;
}
.mt-2 {
  margin-top: 1rem;
}
.mt-3 {
  margin-top: 1.5rem;
}
.mt-4 {
  margin-top: 2rem;
}

.hidden {
  display: none;
}
.visible {
  display: block;
}

/* ===== RESPONSIVE DESIGN ===== */
@media (max-width: 1024px) {
  .container-main {
    width: 90%;
    padding: 0 1.5rem;
  }

  .container-large {
    width: 95%;
    padding: 0 1.5rem;
  }

  .grid-columns-3 {
    grid-template-columns: repeat(2, 1fr);
  }

  .grid-columns-4 {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 768px) {
  .nav-menu {
    position: fixed;
    top: 80px;
    left: -100%;
    width: 100%;
    height: calc(100vh - 80px);
    background-color: rgba(248, 249, 250, 0.98);
    backdrop-filter: blur(10px);
    flex-direction: column;
    justify-content: flex-start;
    padding: 2rem;
    transition: left 0.3s ease;
    z-index: 999;
  }

  .nav-menu.active {
    left: 0;
  }

  .nav-toggle {
    display: flex;
  }

  .nav-social {
    display: none;
  }

  .hero-title {
    font-size: 2.5rem;
  }

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

  .grid-columns-2,
  .grid-columns-3,
  .grid-columns-4 {
    grid-template-columns: 1fr;
  }

  .about-intro {
    grid-template-columns: 1fr;
    text-align: center;
    gap: 2rem;
  }

  .timeline::before {
    left: 20px;
  }

  .timeline-item {
    flex-direction: column !important;
    padding-left: 3rem;
  }

  .timeline-date {
    position: absolute;
    left: 0;
    top: 0;
    width: 40px;
    height: 40px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.8rem;
    margin: 0;
    padding: 0;
  }

  .timeline-content {
    margin-left: 0;
  }

  .contact-content {
    grid-template-columns: 1fr;
    gap: 2rem;
  }

  .model-demo {
    grid-template-columns: 1fr;
  }

  .model-selector {
    position: static;
  }

  .model-stats {
    grid-template-columns: 1fr;
  }

  .footer-content {
    flex-direction: column;
    text-align: center;
  }
}

@media (max-width: 480px) {
  .container-main,
  .container-large {
    padding: 0 1rem;
  }

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

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

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

  .btn {
    padding: 0.6rem 1.5rem;
    font-size: 0.9rem;
  }

  .project-card,
  .publication-item,
  .demo-container {
    padding: 1.5rem;
  }
}

/* ===== ACCESSIBILITY ===== */
@media (prefers-reduced-motion: reduce) {
  * {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }

  html {
    scroll-behavior: auto;
  }
}

/* Focus styles for keyboard navigation */
a:focus,
button:focus,
input:focus,
textarea:focus,
select:focus {
  outline: 2px solid #fd7e14;
  outline-offset: 2px;
}

/* High contrast mode support */
@media (prefers-contrast: high) {
  .btn-primary {
    background-color: #000;
    border-color: #000;
    color: #fff;
  }

  .btn-outline {
    border-color: #000;
    color: #000;
  }

  .btn-outline:hover {
    background-color: #000;
    color: #fff;
  }
}