:root {
  --color-bg: #FFFFFF;
  --color-bg-alt: #F8F9FA;
  --color-text: #1A1A2E;
  --color-text-secondary: #6C757D;
  --color-accent: #2B4C7E;
  --color-accent-hover: #3D6098;
  --color-border: #E9ECEF;
  --color-card-shadow: rgba(0, 0, 0, 0.04);

  --font-heading: 'Source Serif 4', Georgia, serif;
  --font-body: 'Inter', 'Segoe UI', system-ui, sans-serif;

  --max-width: 780px;
  --nav-height: 64px;
  --radius: 6px;
}

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

html {
  font-size: 17px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-body);
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.7;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

a {
  color: var(--color-accent);
  text-decoration: none;
  transition: color 0.2s ease;
}

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

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

h1, h2, h3 {
  font-family: var(--font-heading);
  font-weight: 600;
  line-height: 1.3;
}

h1 { font-size: 2.2rem; }
h2 { font-size: 1.6rem; }
h3 { font-size: 1.15rem; }

/* ─── Navigation ─── */

.nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
}

.nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.5rem;
  height: var(--nav-height);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-name {
  font-family: var(--font-heading);
  font-size: 1.25rem;
  font-weight: 600;
  color: var(--color-text);
}

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

.nav-links {
  display: flex;
  gap: 2rem;
  list-style: none;
}

.nav-links a {
  color: var(--color-text-secondary);
  font-size: 0.92rem;
  font-weight: 500;
  letter-spacing: 0.01em;
  padding: 0.25rem 0;
  border-bottom: 2px solid transparent;
  transition: color 0.2s ease, border-color 0.2s ease;
}

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

.nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.5rem;
  color: var(--color-text);
}

.nav-toggle svg {
  width: 24px;
  height: 24px;
}

/* ─── Main Content ─── */

main {
  flex: 1;
}

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

/* ─── Hero Section (Home) ─── */

.hero {
  padding: 4rem 0 3rem;
}

.hero-inner {
  display: flex;
  align-items: flex-start;
  gap: 3rem;
}

.hero-photo {
  flex-shrink: 0;
  width: 200px;
  height: 200px;
  border-radius: 50%;
  overflow: hidden;
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.08);
}

.hero-photo img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.hero-text {
  flex: 1;
}

.hero-title {
  margin-bottom: 0.25rem;
}

.hero-subtitle {
  font-size: 1.1rem;
  color: var(--color-text-secondary);
  margin-bottom: 0.15rem;
}

.hero-affiliation {
  font-size: 0.95rem;
  color: var(--color-text-secondary);
  margin-bottom: 1.25rem;
}

.hero-bio {
  margin-bottom: 1.5rem;
  color: var(--color-text);
}

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

.hero-links a {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.9rem;
  color: var(--color-accent);
  padding: 0.4rem 0.85rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  transition: background 0.2s ease, border-color 0.2s ease, color 0.2s ease;
}

.hero-links a:hover {
  background: var(--color-bg-alt);
  border-color: var(--color-accent);
}

/* ─── Sections ─── */

.section {
  padding: 2.5rem 0;
}

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

.section-title {
  margin-bottom: 1.5rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--color-border);
}

/* ─── Education ─── */

.education-list {
  list-style: none;
}

.education-list li {
  padding: 0.6rem 0;
  display: flex;
  gap: 0.5rem;
  align-items: baseline;
}

.education-list li + li {
  border-top: 1px solid var(--color-border);
}

.degree {
  font-weight: 600;
  white-space: nowrap;
}

.institution {
  color: var(--color-text-secondary);
}

/* ─── Research Interests ─── */

.interests {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
}

.interest-tag {
  font-size: 0.85rem;
  padding: 0.35rem 0.9rem;
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: 20px;
  color: var(--color-text-secondary);
}

/* ─── Page Header (Research, Data & Code) ─── */

.page-header {
  padding: 3rem 0 1.5rem;
}

.page-header h1 {
  margin-bottom: 0.5rem;
}

.page-header p {
  color: var(--color-text-secondary);
  font-size: 1rem;
}

/* ─── Paper Cards ─── */

.papers-section {
  padding: 2rem 0 3rem;
}

.papers-section + .papers-section {
  border-top: 2px solid var(--color-border);
}

.papers-section-title {
  font-size: 1.35rem;
  margin-bottom: 1.5rem;
  color: var(--color-text);
}

.paper-card {
  padding: 1.5rem 0;
}

.paper-card + .paper-card {
  border-top: 1px solid var(--color-border);
}

.paper-title {
  font-family: var(--font-body);
  font-weight: 600;
  font-size: 1.05rem;
  line-height: 1.5;
  margin-bottom: 0.3rem;
}

.paper-authors {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  margin-bottom: 0.2rem;
}

.paper-venue {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  margin-bottom: 0.6rem;
}

.paper-venue em {
  font-style: italic;
}

.paper-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.75rem;
}

.paper-link {
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--color-accent);
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
}

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

.abstract-toggle {
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--color-accent);
  background: none;
  border: none;
  cursor: pointer;
  padding: 0;
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  font-family: var(--font-body);
  transition: color 0.2s ease;
}

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

.abstract-toggle .chevron {
  display: inline-block;
  transition: transform 0.25s ease;
  font-size: 0.7rem;
}

.abstract-toggle.open .chevron {
  transform: rotate(90deg);
}

.abstract-content {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.35s ease, padding 0.35s ease;
}

.abstract-content.open {
  max-height: 500px;
}

.abstract-text {
  padding: 1rem 0 0.5rem;
  font-size: 0.92rem;
  color: var(--color-text-secondary);
  line-height: 1.7;
  border-left: 3px solid var(--color-border);
  padding-left: 1rem;
}

/* ─── Data & Code Cards ─── */

.data-intro {
  padding: 0 0 1rem;
  color: var(--color-text-secondary);
}

.data-card {
  padding: 1.5rem;
  margin-bottom: 1.25rem;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
}

.data-card-title {
  font-family: var(--font-body);
  font-weight: 600;
  font-size: 1.05rem;
  margin-bottom: 0.25rem;
}

.data-card-ref {
  font-size: 0.88rem;
  color: var(--color-text-secondary);
  margin-bottom: 1rem;
}

.data-items {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.data-link {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.88rem;
  color: var(--color-accent);
  padding: 0.4rem 0.85rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  transition: background 0.2s ease, border-color 0.2s ease;
}

.data-link:hover {
  background: var(--color-bg-alt);
  border-color: var(--color-accent);
}

.data-placeholder {
  padding: 2rem;
  text-align: center;
  color: var(--color-text-secondary);
  background: var(--color-bg-alt);
  border-radius: var(--radius);
  border: 1px dashed var(--color-border);
}

/* ─── Footer ─── */

.footer {
  margin-top: auto;
  padding: 2rem 0;
  border-top: 1px solid var(--color-border);
  color: var(--color-text-secondary);
  font-size: 0.85rem;
}

.footer-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.5rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.footer a {
  color: var(--color-text-secondary);
}

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

/* ─── Responsive ─── */

@media (max-width: 640px) {
  html {
    font-size: 16px;
  }

  h1 { font-size: 1.75rem; }

  .nav-links {
    display: none;
    position: absolute;
    top: var(--nav-height);
    left: 0;
    right: 0;
    flex-direction: column;
    background: var(--color-bg);
    border-bottom: 1px solid var(--color-border);
    padding: 1rem 1.5rem;
    gap: 0;
    box-shadow: 0 4px 12px var(--color-card-shadow);
  }

  .nav-links.open {
    display: flex;
  }

  .nav-links li {
    padding: 0.6rem 0;
  }

  .nav-links li + li {
    border-top: 1px solid var(--color-border);
  }

  .nav-toggle {
    display: block;
  }

  .hero {
    padding: 2.5rem 0 2rem;
  }

  .hero-inner {
    flex-direction: column;
    align-items: center;
    text-align: center;
    gap: 1.5rem;
  }

  .hero-photo {
    width: 160px;
    height: 160px;
  }

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

  .education-list li {
    flex-direction: column;
    gap: 0.1rem;
  }

  .interests {
    justify-content: center;
  }

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

@media (min-width: 641px) and (max-width: 959px) {
  .hero-photo {
    width: 180px;
    height: 180px;
  }
}

/* ─── Print ─── */

@media print {
  .nav, .nav-toggle, .abstract-toggle, .footer {
    display: none;
  }

  .abstract-content {
    max-height: none;
  }

  body {
    font-size: 12pt;
    color: #000;
  }

  a {
    color: #000;
    text-decoration: underline;
  }
}