/* === Reset & Base === */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --color-bg: #ffffff;
  --color-text: #2c2c2c;
  --color-text-secondary: #555;
  --color-accent: #1a5276;
  --color-accent-light: #2980b9;
  --color-border: #e0e0e0;
  --color-bg-alt: #f8f9fa;
  --font-sans: 'Source Sans 3', 'Segoe UI', system-ui, -apple-system, sans-serif;
  --font-serif: 'Source Serif 4', Georgia, 'Times New Roman', serif;
  --max-width: 960px;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: 120px;
}

body {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.7;
  color: var(--color-text);
  background: var(--color-bg);
}

a {
  color: var(--color-accent-light);
  text-decoration: none;
  transition: color 0.15s ease;
}

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

/* === Layout === */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
}

/* === Header / Nav === */
header {
  border-bottom: 1px solid var(--color-border);
  padding: 20px 0;
  position: sticky;
  top: 0;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(8px);
  z-index: 100;
}

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

header h1 {
  font-family: var(--font-serif);
  font-size: 1.3rem;
  font-weight: 600;
  color: var(--color-text);
}

header h1 a {
  color: inherit;
  text-decoration: none;
}

nav ul {
  list-style: none;
  display: flex;
  gap: 28px;
}

nav a {
  color: var(--color-text-secondary);
  font-size: 0.95rem;
  letter-spacing: 0.01em;
}

nav a:hover {
  color: var(--color-text);
  text-decoration: none;
}

/* Mobile nav toggle */
.nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 4px;
}

.nav-toggle span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--color-text);
  margin: 5px 0;
  transition: 0.2s;
}

/* === Sections === */
section {
  padding: 40px 0;
}

section + section {
  border-top: 1px solid var(--color-border);
}

h2 {
  font-family: var(--font-serif);
  font-size: 1.5rem;
  font-weight: 600;
  margin-bottom: 24px;
  color: var(--color-text);
}

/* === About / Hero === */
.about-header {
  display: flex;
  gap: 40px;
  align-items: center;
  margin-bottom: 28px;
}

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

.about-photo img {
  width: 180px;
  height: 180px;
  border-radius: 6px;
  object-fit: cover;
  filter: brightness(0.95);
}

.about-info h2 {
  margin-bottom: 4px;
}

.about-title {
  color: var(--color-text-secondary);
  font-size: 1.05rem;
  margin-bottom: 0;
}

.about-links {
  display: flex;
  gap: 20px;
  margin-top: 12px;
  flex-wrap: wrap;
}

.about-links a {
  font-size: 0.9rem;
}

.about-bio p {
  margin-bottom: 12px;
}

/* === Research Interests === */
.research-list {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.research-list li {
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  padding: 6px 16px;
  border-radius: 4px;
  font-size: 0.92rem;
  color: var(--color-text-secondary);
}

/* === Teaching === */
.teaching-entry h3 {
  font-family: var(--font-serif);
  font-size: 1.2rem;
  font-weight: 600;
  margin-bottom: 8px;
}

.teaching-desc {
  margin-bottom: 8px;
  color: var(--color-text-secondary);
}

.teaching-note {
  margin-bottom: 16px;
  font-size: 0.9rem;
  color: var(--color-text-secondary);
}

.teaching-downloads > p {
  margin-bottom: 8px;
}

.chapter-list {
  margin-top: 6px;
  padding-left: 24px;
}

.chapter-list li {
  margin-bottom: 6px;
  font-size: 0.95rem;
}

/* === Topic Filters === */
.topic-filters {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 32px;
}

.filter-btn {
  padding: 7px 18px;
  border: 1px solid var(--color-border);
  border-radius: 20px;
  background: transparent;
  color: var(--color-text-secondary);
  font-family: var(--font-sans);
  font-size: 0.88rem;
  cursor: pointer;
  transition: background 0.15s ease, color 0.15s ease, border-color 0.15s ease;
}

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

.filter-btn:hover:not(.active) {
  border-color: var(--color-accent-light);
  color: var(--color-accent-light);
}

/* === Topic Groups === */
.topic-group {
  margin-bottom: 40px;
}

.topic-group h3 {
  font-family: var(--font-serif);
  font-size: 1.2rem;
  font-weight: 600;
  margin-bottom: 12px;
}

.topic-group > p {
  color: var(--color-text-secondary);
  font-size: 0.95rem;
  margin-bottom: 20px;
  line-height: 1.7;
}

.topic-group ol {
  padding-left: 24px;
}

.topic-group ol li {
  margin-bottom: 14px;
  font-size: 0.95rem;
}

.topic-group ol li .pub-title {
  font-weight: 600;
}

.topic-group ol li .pub-authors {
  font-size: 0.9rem;
}

.topic-group ol li .pub-links a {
  font-size: 0.85rem;
}

/* === Publications === */
.pub-year-group {
  margin-bottom: 36px;
}

.pub-year-group h3 {
  font-family: var(--font-serif);
  font-size: 1.15rem;
  font-weight: 600;
  color: var(--color-text-secondary);
  margin-bottom: 16px;
  padding-bottom: 6px;
  border-bottom: 1px solid var(--color-border);
}

.pub-entry {
  margin-bottom: 20px;
  padding-left: 0;
}

.pub-title {
  font-weight: 600;
  color: var(--color-text);
  font-size: 1rem;
}

.pub-title a {
  color: var(--color-accent-light);
}

.pub-authors {
  font-size: 0.92rem;
  color: var(--color-text-secondary);
  margin-top: 2px;
}

.pub-authors a {
  color: var(--color-text-secondary);
  text-decoration: underline;
  text-decoration-color: var(--color-border);
  text-underline-offset: 2px;
}

.pub-authors a:hover {
  color: var(--color-accent);
  text-decoration-color: var(--color-accent);
}

.pub-venue {
  font-size: 0.88rem;
  color: var(--color-text-secondary);
  font-style: italic;
  margin-top: 2px;
}

.pub-links {
  margin-top: 4px;
}

.pub-links a {
  font-size: 0.85rem;
  margin-right: 14px;
  color: var(--color-accent-light);
}

.pub-links a::before {
  content: "↓ ";
}

.pub-links a.bibtex-toggle::before,
.pub-links a[href^="https://www.youtube"]::before,
.pub-links a[href^="https://dl.acm"]::before {
  content: "";
}

.bibtex-block {
  display: none;
  margin-top: 8px;
}

.bibtex-block.open {
  display: block;
}

.bibtex-block pre {
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: 4px;
  padding: 12px 16px;
  font-size: 0.82rem;
  line-height: 1.5;
  overflow-x: auto;
  white-space: pre-wrap;
  word-break: break-word;
}

.paper-bibtex {
  margin-top: 32px;
}

.paper-bibtex h3 {
  font-family: var(--font-serif);
  font-size: 1.1rem;
  font-weight: 600;
  margin-bottom: 10px;
  color: var(--color-text-secondary);
}

/* === CV Highlights === */
.cv-section {
  margin-bottom: 32px;
}

.cv-section h3 {
  font-family: var(--font-serif);
  font-size: 1.1rem;
  font-weight: 600;
  margin-bottom: 12px;
  color: var(--color-text-secondary);
  padding-bottom: 4px;
  border-bottom: 1px solid var(--color-border);
}

.cv-table {
  width: 100%;
  border-collapse: collapse;
}

.cv-table td {
  padding: 4px 0;
  vertical-align: top;
  font-size: 0.95rem;
}

.cv-dates {
  width: 130px;
  color: var(--color-text-secondary);
  font-size: 0.9rem;
  white-space: nowrap;
  padding-right: 16px;
}

.cv-pub-list {
  padding-left: 24px;
}

.cv-pub-list li {
  margin-bottom: 8px;
  font-size: 0.95rem;
}

@media (max-width: 640px) {
  .cv-dates {
    width: 110px;
    font-size: 0.85rem;
    padding-right: 12px;
  }
}

/* === Contact === */
.contact-info p {
  margin-bottom: 8px;
}

/* === Footer === */
footer {
  border-top: 1px solid var(--color-border);
  padding: 24px 0;
  text-align: center;
  font-size: 0.85rem;
  color: var(--color-text-secondary);
}

/* === Paper Detail Page === */
.paper-detail {
  padding-top: 40px;
}

.paper-back {
  margin-bottom: 24px;
  font-size: 0.9rem;
}

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

.paper-detail h2 {
  font-size: 1.6rem;
  margin-bottom: 8px;
}

.paper-detail .pub-authors {
  font-size: 1rem;
  margin-bottom: 4px;
}

.paper-detail .pub-venue {
  margin-bottom: 24px;
}

.paper-abstract {
  margin-bottom: 32px;
}

.paper-abstract h3 {
  font-family: var(--font-serif);
  font-size: 1.1rem;
  font-weight: 600;
  margin-bottom: 10px;
  color: var(--color-text-secondary);
}

.paper-abstract p {
  line-height: 1.8;
}

.download-btn {
  display: inline-block;
  padding: 10px 24px;
  background: var(--color-accent);
  color: #fff;
  border-radius: 4px;
  font-size: 0.95rem;
  transition: background 0.15s ease;
}

.download-btn:hover {
  background: var(--color-accent-light);
  text-decoration: none;
  color: #fff;
}

/* === Responsive === */
@media (max-width: 640px) {
  .about-header {
    flex-direction: column;
    align-items: center;
    text-align: center;
  }

  .about-bio {
    text-align: left;
  }

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

  nav ul {
    display: none;
    flex-direction: column;
    gap: 12px;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--color-bg);
    padding: 16px 24px;
    border-bottom: 1px solid var(--color-border);
  }

  nav ul.open {
    display: flex;
  }

  .nav-toggle {
    display: block;
    position: absolute;
    right: 24px;
    top: 50%;
    transform: translateY(-50%);
  }

  header .container {
    position: relative;
  }

  section {
    padding: 40px 0;
  }

  h2 {
    font-size: 1.3rem;
  }

  .filter-btn {
    padding: 5px 12px;
    font-size: 0.78rem;
  }

  .topic-filters {
    gap: 6px;
  }
}