/* 
  Design System & Variables
  -------------------------
*/
:root {
  /* Light Mode Colors */
  --bg-primary: #ffffff;
  --bg-secondary: #f8fafc; /* Slightly off-white for alt sections */
  --bg-card: #ffffff;
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #94a3b8;
  
  /* Accent Color (Professional Blue) */
  --accent: #2563eb;
  --accent-hover: #1d4ed8;
  --accent-light: #dbeafe;
  
  /* Borders & Shadows */
  --border-color: #e2e8f0;
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
  --shadow-hover: 0 20px 25px -5px rgb(0 0 0 / 0.1), 0 8px 10px -6px rgb(0 0 0 / 0.1);
  
  /* Typography */
  --font-main: 'Inter', system-ui, -apple-system, sans-serif;
  
  /* Layout */
  --max-width: 1200px;
  --nav-height: 70px;
  --section-padding: 5rem 0;
  
  /* Animation */
  --transition-fast: 150ms ease;
  --transition-normal: 300ms ease;
  --transition-slow: 500ms ease;
}

/* Dark Mode Colors */
.dark-mode {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-card: #1e293b;
  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #64748b;
  
  --accent: #3b82f6;
  --accent-hover: #60a5fa;
  --accent-light: rgba(59, 130, 246, 0.15);
  
  --border-color: #334155;
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.3);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.4);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.5);
  --shadow-hover: 0 20px 25px -5px rgb(0 0 0 / 0.5);
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: var(--nav-height);
}

body {
  font-family: var(--font-main);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  transition: background-color var(--transition-normal), color var(--transition-normal);
}

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

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

ul {
  list-style: none;
}

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

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 2rem;
}

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

p {
  color: var(--text-secondary);
  margin-bottom: 1rem;
}

.section-title {
  font-size: 2.25rem;
  margin-bottom: 3rem;
  text-align: center;
  position: relative;
}

.section-title::after {
  content: '';
  position: absolute;
  bottom: -0.75rem;
  left: 50%;
  transform: translateX(-50%);
  width: 60px;
  height: 4px;
  background-color: var(--accent);
  border-radius: 2px;
}

.subsection-title {
  font-size: 1.5rem;
  margin-top: 2rem;
  margin-bottom: 1rem;
}

.subsection-title:first-child {
  margin-top: 0;
}

/* 
  Layout & Sections
  -----------------
*/
.section {
  padding: var(--section-padding);
}

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

/* 
  Buttons
  -------
*/
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.75rem 1.5rem;
  font-weight: 500;
  border-radius: 0.375rem;
  cursor: pointer;
  transition: all var(--transition-fast);
  border: 1px solid transparent;
  font-size: 1rem;
}

.btn-primary {
  background-color: var(--accent);
  color: #ffffff;
}

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

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

.btn-secondary:hover {
  background-color: var(--bg-secondary);
  border-color: var(--text-muted);
  transform: translateY(-2px);
}

.btn-block {
  display: block;
  width: 100%;
}

/* 
  Navigation
  ----------
*/
.navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background-color: rgba(var(--bg-primary-rgb), 0.9);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border-color);
  z-index: 1000;
  transition: background-color var(--transition-normal);
}

.nav-content {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 2rem;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

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

.nav-links {
  display: flex;
  align-items: center;
  gap: 1.5rem;
}

.nav-links a {
  color: var(--text-secondary);
  font-weight: 500;
  font-size: 0.9rem;
  padding: 0.5rem;
  position: relative;
}

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

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

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

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

.theme-toggle:hover {
  background-color: var(--bg-secondary);
  color: var(--text-primary);
}

.hamburger {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.5rem;
}

.hamburger span {
  display: block;
  width: 24px;
  height: 2px;
  background-color: var(--text-primary);
  margin-bottom: 5px;
  transition: transform var(--transition-fast), opacity var(--transition-fast);
}

/* 
  Loading State
  -------------
*/
.loading-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100vh;
}

.spinner {
  width: 40px;
  height: 40px;
  border: 4px solid var(--border-color);
  border-top: 4px solid var(--accent);
  border-radius: 50%;
  animation: spin 1s linear infinite;
  margin-bottom: 1rem;
}

@keyframes spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}

/* 
  Hero Section
  ------------
*/
.hero-section {
  padding-top: calc(var(--nav-height) + 4rem);
  padding-bottom: 4rem;
  min-height: 100vh;
  display: flex;
  align-items: center;
  max-width: var(--max-width);
  margin: 0 auto;
  padding-left: 2rem;
  padding-right: 2rem;
}

.hero-content {
  flex: 1;
  padding-right: 2rem;
}

.hero-title {
  font-size: 3.5rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
}

.hero-subtitle {
  font-size: 1.75rem;
  color: var(--accent);
  font-weight: 500;
  margin-bottom: 1.5rem;
}

.hero-intro {
  font-size: 1.125rem;
  margin-bottom: 2rem;
  max-width: 600px;
}

.hero-ctas {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
}

.hero-image-container {
  flex: 1;
  display: flex;
  justify-content: center;
  align-items: center;
}

.hero-image {
  max-width: 400px;
  width: 100%;
  border-radius: 1rem;
  box-shadow: var(--shadow-lg);
  border: 1px solid var(--border-color);
}

/* 
  Cards & Grid Base
  -----------------
*/
.card {
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: 0.5rem;
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition-normal), box-shadow var(--transition-normal);
}

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

/* About Section */
.about-grid {
  display: grid;
  grid-template-columns: 2fr 1fr;
  gap: 3rem;
}

.interest-list {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.interest-list li {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.interest-list li::before {
  content: '→';
  color: var(--accent);
}

/* Skills Section */
.skills-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.5rem;
}

.skill-category-title {
  font-size: 1.125rem;
  margin-bottom: 1rem;
  color: var(--text-primary);
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 0.5rem;
}

.skill-chips {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.skill-chip {
  background-color: var(--accent-light);
  color: var(--accent);
  padding: 0.25rem 0.75rem;
  border-radius: 9999px;
  font-size: 0.875rem;
  font-weight: 500;
}

/* Timeline (Experience & Education) */
.timeline {
  position: relative;
  max-width: 800px;
  margin: 0 auto;
}

.timeline::before {
  content: '';
  position: absolute;
  top: 0;
  bottom: 0;
  left: 1.5rem;
  width: 2px;
  background-color: var(--border-color);
}

.timeline-item {
  position: relative;
  padding-left: 4rem;
  margin-bottom: 3rem;
}

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

.timeline-dot {
  position: absolute;
  left: 1rem;
  top: 0.25rem;
  width: 1rem;
  height: 1rem;
  border-radius: 50%;
  background-color: var(--accent);
  border: 3px solid var(--bg-primary);
  box-shadow: 0 0 0 2px var(--accent-light);
}

.timeline-content {
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: 0.5rem;
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
}

.timeline-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: 0.5rem;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.timeline-title {
  font-size: 1.25rem;
  font-weight: 600;
}

.timeline-org {
  font-weight: 500;
  color: var(--accent);
}

.timeline-date {
  font-size: 0.875rem;
  color: var(--text-muted);
  background-color: var(--bg-secondary);
  padding: 0.25rem 0.5rem;
  border-radius: 0.25rem;
}

.timeline-details {
  margin-top: 1rem;
}

.timeline-details ul {
  list-style-type: disc;
  padding-left: 1.5rem;
  color: var(--text-secondary);
}

.timeline-details li {
  margin-bottom: 0.25rem;
}

/* Projects */
.filters {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-bottom: 2rem;
}

.filter-btn {
  background: transparent;
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  padding: 0.5rem 1rem;
  border-radius: 9999px;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.filter-btn:hover, .filter-btn.active {
  background-color: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

.projects-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 2rem;
}

.project-card {
  display: flex;
  flex-direction: column;
  overflow: hidden;
  padding: 0;
}

.project-img-container {
  height: 200px;
  overflow: hidden;
  border-bottom: 1px solid var(--border-color);
}

.project-img-container img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform var(--transition-normal);
}

.project-card:hover .project-img-container img {
  transform: scale(1.05);
}

.project-content {
  padding: 1.5rem;
  flex: 1;
  display: flex;
  flex-direction: column;
}

.project-title {
  font-size: 1.25rem;
  margin-bottom: 0.5rem;
}

.project-desc {
  flex: 1;
  margin-bottom: 1rem;
  font-size: 0.95rem;
}

.project-tech {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-bottom: 1rem;
}

.project-tech span {
  font-size: 0.75rem;
  padding: 0.15rem 0.5rem;
  background-color: var(--bg-secondary);
  border-radius: 4px;
  color: var(--text-secondary);
}

.project-links {
  display: flex;
  gap: 1rem;
  margin-top: auto;
}

.project-links a {
  font-size: 0.875rem;
  font-weight: 500;
  display: flex;
  align-items: center;
  gap: 0.25rem;
}

/* Certifications */
.certifications-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.5rem;
}

.cert-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: 1rem;
}

.cert-content {
  width: 100%;
}

.cert-icon {
  width: 48px;
  height: 48px;
  background-color: var(--accent-light);
  color: var(--accent);
  border-radius: 0.5rem;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.cert-img-container {
  width: 100%;
  max-width: 180px;
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background-color: transparent;
  margin: 0 auto 1rem auto;
  transition: transform 0.3s ease;
}

.cert-img-container:hover {
  transform: scale(1.05);
}

.cert-img {
  width: 100%;
  height: auto;
  object-fit: contain;
}



.cert-content h3 {
  font-size: 1.125rem;
  margin-bottom: 0.25rem;
}

.cert-content p {
  font-size: 0.875rem;
  margin-bottom: 0;
}

.cert-link {
  font-size: 0.875rem;
  margin-top: 0.5rem;
  display: inline-block;
}

/* Publications */
.publications-list {
  display: grid;
  gap: 1.5rem;
}

.pub-card {
  padding: 1.5rem;
}

.pub-title {
  font-size: 1.25rem;
  margin-bottom: 0.5rem;
}

.pub-authors {
  font-style: italic;
  margin-bottom: 0.5rem;
}

.pub-meta {
  font-size: 0.875rem;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

.pub-links {
  display: flex;
  gap: 1rem;
}

/* Contact */
.contact-grid {
  display: grid;
  grid-template-columns: 1fr 1.5fr;
  gap: 3rem;
}

.contact-links {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  margin-top: 2rem;
}

.contact-link-item {
  display: flex;
  align-items: center;
  gap: 1rem;
  color: var(--text-primary);
  font-size: 1.125rem;
}

.contact-icon {
  width: 40px;
  height: 40px;
  background-color: var(--bg-secondary);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--accent);
}

.contact-form {
  background-color: var(--bg-card);
  padding: 2rem;
  border-radius: 0.5rem;
  border: 1px solid var(--border-color);
  box-shadow: var(--shadow-sm);
}

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

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

.form-group input,
.form-group textarea {
  width: 100%;
  padding: 0.75rem;
  border: 1px solid var(--border-color);
  border-radius: 0.375rem;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-family: inherit;
  transition: border-color var(--transition-fast);
}

.form-group input:focus,
.form-group textarea:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-light);
}

/* Footer */
.footer {
  text-align: center;
  padding: 2rem 0;
  border-top: 1px solid var(--border-color);
  background-color: var(--bg-primary);
}

/* 
  Responsive Design
  -----------------
*/
@media (max-width: 992px) {
  .hero-section {
    flex-direction: column-reverse;
    text-align: center;
    padding-top: calc(var(--nav-height) + 2rem);
  }
  
  .hero-content {
    padding-right: 0;
    margin-top: 2rem;
  }
  
  .hero-intro {
    margin: 0 auto 2rem;
  }
  
  .hero-ctas {
    justify-content: center;
  }
  
  .about-grid,
  .contact-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 768px) {
  .section {
    padding: 3rem 0;
  }
  
  .hamburger {
    display: block;
  }
  
  .nav-links {
    position: absolute;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background-color: var(--bg-primary);
    flex-direction: column;
    padding: 1rem;
    gap: 0;
    border-bottom: 1px solid var(--border-color);
    box-shadow: var(--shadow-md);
    transform: translateY(-150%);
    transition: transform var(--transition-normal);
    z-index: -1;
  }
  
  .nav-links.show {
    transform: translateY(0);
  }
  
  .nav-links a {
    display: block;
    width: 100%;
    padding: 1rem;
    text-align: center;
  }
  
  .nav-links a::after {
    display: none;
  }
  
  .timeline::before {
    left: 1rem;
  }
  
  .timeline-item {
    padding-left: 3rem;
  }
  
  .timeline-dot {
    left: 0.5rem;
  }
  
  .hero-title {
    font-size: 2.5rem;
  }
  
  .hero-subtitle {
    font-size: 1.25rem;
  }
}