/* ===== CSS Custom Properties (Design Tokens) ===== */
:root {
  /* Colors - Light Mode */
  --bg-primary: #ffffff;
  --bg-secondary: #f8fafc;
  --bg-tertiary: #f1f5f9;
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-tertiary: #64748b;
  --border-color: #e2e8f0;
  --accent: #10b981;
  --accent-hover: #059669;
  --accent-subtle: rgba(16, 185, 129, 0.1);

  /* Shadows */
  --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 -2px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -4px rgba(0, 0, 0, 0.1);

  /* Spacing */
  --container-max: 1100px;
  --section-spacing: 4rem;

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 350ms ease;

  /* Border Radius */
  --radius-sm: 0.375rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --radius-xl: 1rem;
  --radius-full: 9999px;
}

/* Dark Mode */
[data-theme="dark"] {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-tertiary: #334155;
  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-tertiary: #94a3b8;
  --border-color: #334155;
  --accent: #34d399;
  --accent-hover: #6ee7b7;
  --accent-subtle: rgba(52, 211, 153, 0.15);

  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4), 0 2px 4px -2px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4), 0 4px 6px -4px rgba(0, 0, 0, 0.3);
}

/* ===== Base Reset & Typography ===== */
*, *::before, *::after {
  box-sizing: border-box;
}

html {
  padding: 0;
  margin: 0;
  scroll-behavior: smooth;
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  margin: 0;
  padding: 0;
  transition: background-color var(--transition-base), color var(--transition-base);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* ===== Layout ===== */
.container {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 1.5rem;
}

.clearfix {
  clear: both;
}

/* ===== Navigation ===== */
#nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1.5rem 0;
  position: sticky;
  top: 0;
  background: var(--bg-primary);
  z-index: 100;
  border-bottom: 1px solid var(--border-color);
  margin-bottom: 2rem;
  backdrop-filter: blur(8px);
  background: rgba(var(--bg-primary), 0.8);
}

[data-theme="dark"] #nav {
  background: rgba(15, 23, 42, 0.9);
}

[data-theme="light"] #nav {
  background: rgba(255, 255, 255, 0.9);
}

#menu ul {
  display: flex;
  gap: 2rem;
  list-style: none;
  margin: 0;
  padding: 0;
}

#menu ul li {
  margin: 0;
}

#menu ul li a {
  font-size: 0.9rem;
  font-weight: 500;
  text-decoration: none;
  color: var(--text-secondary);
  transition: color var(--transition-fast);
  letter-spacing: -0.01em;
}

#menu ul li a:hover {
  color: var(--accent);
}

#social-links {
  display: flex;
  align-items: center;
  gap: 1rem;
}

#social-links a {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: var(--radius-md);
  transition: background-color var(--transition-fast), transform var(--transition-fast);
}

#social-links a:hover {
  background-color: var(--bg-tertiary);
  transform: translateY(-2px);
}

#social-links img {
  width: 28px;
  height: 28px;
  opacity: 0.7;
  transition: opacity var(--transition-fast);
}

#social-links a:hover img {
  opacity: 1;
}

/* Business Card Icon */
.businesscard-icon .bc-text {
  fill: #100e2d;
}

.businesscard-icon .bc-dot {
  fill: #10b981;
}

[data-theme="dark"] .businesscard-icon .bc-text {
  fill: #e2e8f0;
}

/* Dark Mode Toggle */
.theme-toggle {
  background: var(--bg-tertiary);
  border: none;
  border-radius: var(--radius-full);
  padding: 0.5rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  transition: background-color var(--transition-fast), transform var(--transition-fast);
}

.theme-toggle:hover {
  background: var(--border-color);
  transform: scale(1.05);
}

.theme-toggle svg {
  width: 20px;
  height: 20px;
  color: var(--text-secondary);
}

.theme-toggle .sun-icon {
  display: none;
}

.theme-toggle .moon-icon {
  display: block;
}

[data-theme="dark"] .theme-toggle .sun-icon {
  display: block;
}

[data-theme="dark"] .theme-toggle .moon-icon {
  display: none;
}

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

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

.emphasis {
  background: var(--accent-subtle);
  color: var(--accent);
  padding: 0.125rem 0.5rem;
  border-radius: var(--radius-sm);
  font-weight: 500;
  text-decoration: none;
  transition: background-color var(--transition-fast), color var(--transition-fast);
}

a.emphasis:hover,
span.emphasis:hover {
  background: var(--accent);
  color: white;
}

/* ===== Hero Section (Home) ===== */
.hero {
  padding: 3rem 0 4rem;
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: -50px;
  right: -100px;
  width: 400px;
  height: 400px;
  background: radial-gradient(circle, var(--accent-subtle) 0%, transparent 70%);
  z-index: -1;
  opacity: 0.7;
}

.hero-content {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 3rem;
  align-items: stretch;
}

.hero-image {
  display: flex;
  align-items: stretch;
}

#profile-photo {
  width: auto;
  height: 100%;
  max-width: 280px;
  object-fit: cover;
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-lg);
  transition: transform var(--transition-base), box-shadow var(--transition-base);
}

#profile-photo:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg), 0 20px 40px -15px rgba(16, 185, 129, 0.2);
}

/* QR Code Card */
.qr-card {
  margin-top: 2rem;
  padding: 1.5rem;
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  display: inline-block;
  text-align: center;
  transition: transform var(--transition-base), box-shadow var(--transition-base), border-color var(--transition-fast);
}

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

.qr-card img {
  width: 140px;
  height: 140px;
  border-radius: var(--radius-md);
  transition: transform var(--transition-base);
}

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

.qr-card span {
  display: block;
  margin-top: 0.75rem;
  font-size: 0.875rem;
  color: var(--text-tertiary);
}

.hero h1 {
  font-size: 2.75rem;
  font-weight: 700;
  letter-spacing: -0.03em;
  line-height: 1.1;
  margin: 0 0 0.5rem;
  color: var(--text-primary);
}

.hero-tagline {
  font-size: 1.25rem;
  color: var(--text-secondary);
  margin: 0 0 1.5rem;
  line-height: 1.5;
  font-weight: 400;
}

#bio {
  width: 100%;
}

#bio p,
#about p {
  font-size: 1.05rem;
  line-height: 1.75;
  color: var(--text-secondary);
  margin: 0 0 1rem;
}

#bio p:last-child {
  margin-bottom: 0;
}

/* ===== Page Titles ===== */
h1 {
  font-size: 2.5rem;
  font-weight: 700;
  letter-spacing: -0.03em;
  margin: 0 0 0.5rem;
  color: var(--text-primary);
}

h2 {
  font-size: 1.25rem;
  font-weight: 400;
  color: var(--text-secondary);
  margin: 0 0 2rem;
  line-height: 1.5;
}

.page-title {
  margin: 0 0 2rem;
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--border-color);
}

.page-title h3 {
  font-size: 1.75rem;
  font-weight: 600;
  letter-spacing: -0.02em;
  margin: 0;
  color: var(--text-primary);
  background: none;
  text-transform: none;
  width: auto;
}

/* ===== Page Intro ===== */
.page-intro {
  color: var(--text-tertiary);
  font-style: italic;
  margin: 0 0 1rem;
  font-size: 1rem;
  line-height: 1.6;
}

/* ===== Section Headers ===== */
h4.category {
  font-size: 1.25rem;
  font-weight: 600;
  color: var(--text-primary);
  margin: 3rem 0 1.5rem;
  padding-bottom: 0.75rem;
  border-bottom: 2px solid var(--accent);
  display: inline-block;
}

/* ===== Books Section ===== */
ol.books, ul.books {
  margin: 1rem 0 0 1.5rem;
  padding: 0;
}

ol.books li, ul.books li {
  padding: 0.4rem 0;
  color: var(--text-secondary);
  line-height: 1.5;
}

ol.books li::marker {
  color: var(--text-tertiary);
  font-size: 0.9rem;
}

ol.books li a, ul.books li a {
  font-weight: 500;
  font-size: 1rem;
  color: var(--text-primary);
  text-decoration: none;
  transition: color var(--transition-fast);
}

ol.books li a:hover, ul.books li a:hover {
  color: var(--accent);
}

ol.books li a.emphasis {
  background: var(--accent);
  color: white;
  padding: 0.125rem 0.5rem;
  border-radius: var(--radius-sm);
}

ol.books li a.emphasis:hover {
  background: var(--accent-hover);
}

/* ===== Travels Section ===== */
#travels {
  margin: 2rem 0;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.5rem;
}

.travel {
  float: none;
  width: auto;
  height: auto;
  padding: 0;
  margin: 0;
  background: var(--bg-secondary);
  border-radius: var(--radius-lg);
  overflow: hidden;
  border: 1px solid var(--border-color);
  transition: transform var(--transition-base), box-shadow var(--transition-base), border-color var(--transition-fast);
}

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

.travel .fancybox img {
  width: 100%;
  height: 200px;
  object-fit: cover;
  display: block;
  transition: transform var(--transition-slow);
}

.travel:hover .fancybox img {
  transform: scale(1.05);
}

.travel .fancybox {
  display: block;
  overflow: hidden;
}

.travel-info {
  padding: 1rem;
}

.travel .location {
  font-weight: 600;
  color: var(--text-primary);
  margin: 0;
  padding: 1rem 1rem 0.25rem;
}

.travel .date {
  font-size: 0.875rem;
  color: var(--text-tertiary);
  padding: 0 1rem 1rem;
}

/* ===== Resume Section ===== */
#resume {
  width: 100%;
}

.work-experience, .education {
  margin: 0 0 2.5rem;
  padding: 1.5rem;
  background: var(--bg-secondary);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
  transition: border-color var(--transition-fast);
}

.work-experience:hover, .education:hover {
  border-color: var(--accent);
}

#resume .date {
  float: none;
  width: auto;
  text-align: left;
  font-size: 0.875rem;
  color: var(--text-tertiary);
  margin-bottom: 0.5rem;
}

#resume h5 {
  font-size: 1.25rem;
  font-weight: 600;
  margin: 0 0 0.25rem;
  color: var(--text-primary);
}

#resume h5 a {
  color: var(--text-primary);
}

#resume h5 a:hover {
  color: var(--accent);
}

#resume h6 {
  font-size: 1rem;
  font-weight: 500;
  color: var(--text-secondary);
  margin: 0 0 1rem;
}

.work-experience ul {
  margin: 0;
  padding-left: 1.25rem;
}

.work-experience li {
  margin-bottom: 0.75rem;
  font-size: 0.95rem;
  line-height: 1.6;
  color: var(--text-secondary);
}

.work-experience li:last-child {
  margin-bottom: 0;
}

/* ===== Tags ===== */
.tag {
  display: inline-block;
  margin-left: 0.5rem;
  padding: 0.125rem 0.5rem;
  background: var(--accent-subtle);
  color: var(--accent);
  font-size: 0.75rem;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.025em;
  border-radius: var(--radius-sm);
}

/* ===== Languages & Conferences ===== */
ul.languages, ul.conferences {
  list-style: none;
  margin: 1.5rem 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
}

ul.languages li, ul.conferences li {
  float: none;
  display: inline-flex;
  align-items: center;
  padding: 0.5rem 1rem;
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-full);
  font-size: 0.9rem;
  transition: border-color var(--transition-fast), transform var(--transition-fast);
}

ul.languages li:hover, ul.conferences li:hover {
  border-color: var(--accent);
  transform: translateY(-2px);
}

/* ===== Honors ===== */
.honors {
  margin: 1rem 0;
  padding: 1rem 1.25rem;
  background: var(--bg-secondary);
  border-radius: var(--radius-md);
  border-left: 3px solid var(--accent);
}

.honors .date {
  font-size: 0.875rem;
  color: var(--text-tertiary);
  margin-bottom: 0.25rem;
}

.honors h6 {
  margin: 0;
  font-size: 1rem;
  font-weight: 500;
  color: var(--text-primary);
}

/* ===== Other Studies ===== */
#other-studies + .education,
.education + .education {
  margin-top: 1.5rem;
}

/* ===== Presentations ===== */
#presentations {
  margin: 2rem 0;
}

.presentation {
  padding: 1.5rem;
  margin-bottom: 1.5rem;
  background: var(--bg-secondary);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
}

/* ===== Responsive ===== */
@media screen and (max-width: 768px) {
  .hero-content {
    grid-template-columns: 1fr;
    text-align: center;
  }

  .hero-image {
    justify-content: center;
  }

  #profile-photo {
    max-width: 200px;
    height: auto;
    margin: 0 auto;
  }

  .hero h1 {
    font-size: 2rem;
  }

  #nav {
    flex-direction: column;
    gap: 1rem;
    position: relative;
  }

  #menu ul {
    gap: 1rem;
    flex-wrap: wrap;
    justify-content: center;
  }

  #social-links {
    order: -1;
  }

  #travels {
    grid-template-columns: 1fr;
  }

  .work-experience, .education {
    padding: 1rem;
  }

  h1 {
    font-size: 2rem;
  }

  h4.category {
    font-size: 1.1rem;
  }
}

@media screen and (max-width: 480px) {
  .container {
    padding: 0 1rem;
  }

  #menu ul {
    gap: 0.75rem;
  }

  #menu ul li a {
    font-size: 0.85rem;
  }

  .hero h1 {
    font-size: 1.75rem;
  }

  #bio p, #about p {
    font-size: 0.95rem;
  }
}

/* ===== Footer ===== */
.site-footer {
  margin-top: 4rem;
  padding: 2rem 0;
  border-top: 1px solid var(--border-color);
}

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

.footer-content .copyright {
  margin: 0;
  font-size: 0.875rem;
  color: var(--text-tertiary);
}

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

.footer-links a {
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-tertiary);
  transition: color var(--transition-fast), transform var(--transition-fast);
}

.footer-links a:hover {
  color: var(--accent);
  transform: translateY(-2px);
}

.footer-links svg {
  width: 28px;
  height: 28px;
}


@media screen and (max-width: 480px) {
  .footer-content {
    flex-direction: column;
    gap: 1rem;
    text-align: center;
  }
}

/* ===== Utility Classes ===== */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}