/* ===== Spatial-TTT — Premium project page (white theme like OmniVGGT) ===== */
:root {
  --color-bg: #ffffff;
  --color-bg-alt: #f7fafc;
  --color-surface: #ffffff;
  --color-text: #1a202c;
  --color-text-muted: #4a5568;
  --color-accent: #34588e;
  --color-accent-hover: #2a4670;
  --color-hero-border: #e2e8f0;
  --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  --font-display: var(--font-family);
  --font-body: var(--font-family);
  --radius: 12px;
  --radius-lg: 20px;
  --shadow: 0 4px 24px rgba(0, 0, 0, 0.06);
  --shadow-lg: 0 12px 48px rgba(0, 0, 0, 0.08);
  --max-width: 960px;
  --max-width-wide: 1120px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: var(--font-body);
  font-size: 17px;
  line-height: 1.65;
  color: var(--color-text);
  background: var(--color-bg);
  -webkit-font-smoothing: antialiased;
}

/* ----- Top Navigation (like 4DGS) ----- */
.top-nav {
  background: var(--color-bg);
  padding: 15px 20px;
}

.nav-inner {
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 20px;
}

.nav-home {
  color: #4a5568;
  text-decoration: none;
  font-size: 1.1em;
  transition: color 0.2s;
}

.nav-home:hover {
  color: var(--color-text);
}

.nav-dropdown {
  position: relative;
}

.nav-dropdown-btn {
  font-family: inherit;
  font-size: 1em;
  font-weight: 400;
  color: #42a5f5;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 6px;
}

.nav-dropdown-btn .nav-arrow {
  font-size: 0.7em;
  transition: transform 0.2s;
}

.nav-dropdown:hover .nav-dropdown-btn .nav-arrow {
  transform: rotate(180deg);
}

.nav-dropdown-content {
  position: absolute;
  top: 100%;
  left: 0;
  background: var(--color-bg);
  border: 1px solid var(--color-hero-border);
  border-radius: 4px;
  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.1);
  min-width: 220px;
  padding: 8px 0;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.15s, visibility 0.15s;
  z-index: 100;
  margin-top: 5px;
}

.nav-dropdown:hover .nav-dropdown-content {
  opacity: 1;
  visibility: visible;
}

.nav-dropdown-content a {
  display: block;
  padding: 8px 16px;
  color: var(--color-text);
  text-decoration: none;
  font-size: 0.95em;
  transition: background 0.15s;
}

.nav-dropdown-content a:hover {
  background: #f5f5f5;
}

/* ----- Hero (white background like OmniVGGT) ----- */
.hero {
  background: var(--color-bg);
  text-align: center;
  padding: 60px 40px 40px;
  border-bottom: 1px solid var(--color-hero-border);
  color: #2d3748;
}

.hero-inner {
  max-width: 1000px;
  margin: 0 auto;
  text-align: center;
}

/* Title style like Spatial-MLLM: two lines, project name in blue-purple */
.hero-title {
  font-family: var(--font-display);
  font-size: clamp(2rem, 5vw, 2.6em);
  font-weight: 700;
  letter-spacing: -0.02em;
  margin: 0 0 1rem;
  line-height: 1.3;
}

.hero-title .title-line1 {
  display: block;
  white-space: nowrap;
}

.hero-title .title-line2 {
  display: block;
  color: var(--color-text);
  font-weight: 600;
}

.hero-title .title-project {
  color: #5b8fc9;
}

.hero-title .title-rest {
  color: var(--color-text);
  font-weight: 600;
}

.hero-authors {
  margin: 0 auto 1.25rem;
  font-size: 1.05em;
  line-height: 1.8;
  color: #2d3748;
  max-width: 900px;
}

.hero-authors .author-list {
  display: block;
  margin-bottom: 0.5em;
}

.hero-authors a {
  color: var(--color-accent);
  text-decoration: none;
  border-bottom: 1px solid rgba(52, 88, 142, 0.3);
  transition: border-color 0.2s, color 0.2s;
}

.hero-authors a:hover {
  border-bottom-color: var(--color-accent);
  color: var(--color-accent-hover);
}

.hero-affiliations {
  display: block;
  color: #718096;
  font-size: 0.95em;
  margin: 0.75em 0 0;
  line-height: 1.6;
}

.hero-notes {
  display: block;
  color: #718096;
  font-size: 0.85rem;
  margin: 0.35em 0 0;
}

/* Institution logos: below affiliations, with hover effect like OmniVGGT */
.hero-logos {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 30px;
  margin: 30px auto;
  max-width: 1200px;
}

.hero-logo-link {
  display: flex;
  align-items: center;
  text-decoration: none;
  transition: transform 0.3s ease;
}

.hero-logo-link:hover {
  transform: scale(1.1);
}

.hero-logo-link:active {
  transform: scale(1.05);
}

.hero-logo-img {
  height: 60px;
  width: auto;
  max-width: 180px;
  object-fit: contain;
  object-position: center;
  filter: grayscale(30%);
  transition: filter 0.3s ease;
}

.hero-logo-link:hover .hero-logo-img {
  filter: grayscale(0%);
}

.hero-links {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  justify-content: center;
  margin-top: 30px;
}

.hero-link {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 10px 20px;
  background: #f3f4f6;
  color: #374151;
  text-decoration: none;
  font-weight: 500;
  font-size: 0.9em;
  border-radius: 8px;
  border: 1px solid #e5e7eb;
  transition: background 0.2s ease, border-color 0.2s ease;
}

.hero-link:hover {
  background: #e5e7eb;
  border-color: #d1d5db;
  color: #1f2937;
}

.hero-link .icon {
  font-size: 1em;
  display: inline-flex;
  align-items: center;
}

.hero-link .hf-icon {
  vertical-align: middle;
}

.hero-link .hf-logo {
  width: 1.1em;
  height: 1.1em;
  vertical-align: middle;
}

/* ----- Sections ----- */
.section {
  padding: 4rem 1.5rem;
}

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

.container {
  max-width: var(--max-width-wide);
  margin: 0 auto;
}

.container-narrow {
  max-width: var(--max-width);
}

.section-title {
  font-family: var(--font-display);
  font-size: clamp(1.75rem, 3vw, 2.25rem);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--color-text);
  margin: 0 0 0.75rem;
}

.section-lead {
  font-size: 1.05rem;
  color: var(--color-text-muted);
  margin: 0 0 2.5rem;
  max-width: 640px;
  line-height: 1.6;
}

/* ----- Teaser ----- */
.section-teaser {
  padding-top: 3rem;
}

.teaser-wrap {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  box-shadow: var(--shadow);
}

.teaser-img {
  width: 100%;
  height: auto;
  display: block;
  border-radius: var(--radius);
  margin-bottom: 1.25rem;
}

.teaser-caption {
  margin: 0;
  font-size: 1rem;
  color: var(--color-text-muted);
  line-height: 1.65;
}

/* ----- Abstract ----- */
.abstract-text {
  font-size: 1.05rem;
}

.abstract-text p {
  margin: 0 0 1rem;
}

.abstract-text p:last-child {
  margin-bottom: 0;
}

.abstract-text em {
  font-style: italic;
  color: var(--color-text);
}

.abstract-text strong {
  font-weight: 600;
  color: var(--color-text);
}

/* ----- Video Demo ----- */
.video-wrapper {
  position: relative;
  width: 100%;
  padding-bottom: 56.25%; /* 16:9 aspect ratio */
  margin: 1.5rem 0;
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-lg);
}

.video-wrapper iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  border: none;
}

.video-caption {
  text-align: center;
  font-size: 0.95rem;
  color: var(--color-text-muted);
  margin-top: 1rem;
}

/* ----- Contributions ----- */
.contrib-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.5rem;
  margin-top: 1rem;
}

.contrib-card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  box-shadow: var(--shadow);
  border: 1px solid rgba(0, 0, 0, 0.04);
  transition: box-shadow 0.25s, transform 0.2s;
}

.contrib-card:hover {
  box-shadow: var(--shadow-lg);
  transform: translateY(-2px);
}

.contrib-icon {
  font-size: 1.75rem;
  margin-bottom: 0.75rem;
}

.contrib-card h3 {
  font-family: var(--font-display);
  font-size: 1.2rem;
  font-weight: 700;
  margin: 0 0 0.5rem;
  color: var(--color-text);
}

.contrib-card p {
  margin: 0;
  font-size: 0.95rem;
  color: var(--color-text-muted);
  line-height: 1.6;
}

/* ----- Method / Results ----- */
.figure-block {
  margin: 1.5rem 0 2.5rem;
}

.figure-block:last-child {
  margin-bottom: 0;
}

.figure-img {
  width: 100%;
  height: auto;
  display: block;
  border-radius: var(--radius);
  mix-blend-mode: multiply;
  background: var(--color-surface);
}

.figure-caption {
  margin: 1rem 0 0;
  font-size: 0.95rem;
  color: var(--color-text-muted);
  line-height: 1.65;
}

.result-block {
  margin-bottom: 3rem;
}

.result-block:last-child {
  margin-bottom: 0;
}

.result-heading {
  font-family: var(--font-display);
  font-size: 1.35rem;
  font-weight: 700;
  margin: 0 0 0.5rem;
  color: var(--color-text);
}

.result-desc {
  margin: 0 0 1rem;
  font-size: 0.98rem;
  color: var(--color-text-muted);
  line-height: 1.6;
}

/* ----- Citation ----- */
.section-citation {
  background: var(--color-bg-alt);
}

.bibtex {
  margin: 0;
  padding: 1.25rem 1.5rem;
  background: var(--color-surface);
  border-radius: var(--radius);
  border: 1px solid rgba(0, 0, 0, 0.06);
  overflow-x: auto;
  font-family: 'SF Mono', 'Monaco', 'Consolas', monospace;
  font-size: 0.85rem;
  line-height: 1.6;
  color: var(--color-text);
}

.bibtex code {
  background: none;
  padding: 0;
}

/* ----- Footer (light like OmniVGGT) ----- */
.footer {
  padding: 30px 1.5rem;
  background: var(--color-bg-alt);
  color: var(--color-text-muted);
  text-align: center;
  font-size: 0.95em;
  border-top: 1px solid var(--color-hero-border);
  margin-top: 60px;
}

.footer-text {
  margin: 0;
  font-size: 0.95rem;
}

.footer-sub {
  margin-top: 10px;
  font-size: 0.9rem;
  opacity: 0.8;
}

/* ----- Responsive ----- */
@media (max-width: 640px) {
  .hero {
    padding: 40px 20px 30px;
  }

  .hero-logos {
    gap: 20px;
    margin: 20px auto;
  }

  .hero-logo-img {
    height: 50px;
  }

  .section {
    padding: 3rem 1rem;
  }

  .contrib-grid {
    grid-template-columns: 1fr;
  }
}