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

:root {
  --bg: #0f0f0f;
  --surface: #1a1a1a;
  --surface-hover: #242424;
  --border: #2a2a2a;
  --text: #e0e0e0;
  --text-muted: #888;
  --accent: #6c9bff;
  --accent-hover: #8ab4ff;
  --tag-bg: #1e2a3a;
  --tag-text: #6c9bff;
  --radius: 10px;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

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

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

/* ===== Header ===== */
header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(15, 15, 15, 0.9);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
}

.header-inner {
  max-width: 1100px;
  margin: 0 auto;
  padding: 14px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.logo {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--text);
  letter-spacing: -0.5px;
}

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

.logo-icon {
  font-size: 1.4rem;
}

.header-nav {
  display: flex;
  align-items: center;
  gap: 16px;
}

.nav-link {
  color: var(--text-muted);
  font-size: 0.9rem;
  font-weight: 500;
  padding: 4px 8px;
  border-radius: 6px;
  transition: color 0.2s;
}

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

.nav-link.active {
  color: var(--accent);
}

.lang-btn {
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 6px 14px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.85rem;
  transition: all 0.2s;
}

.lang-btn:hover {
  background: var(--surface-hover);
  border-color: var(--accent);
}

/* ===== Hero ===== */
.hero {
  text-align: center;
  padding: 64px 24px 36px;
}

.hero h1 {
  font-size: 2.5rem;
  font-weight: 800;
  letter-spacing: -1px;
  margin-bottom: 12px;
}

.hero p {
  color: var(--text-muted);
  font-size: 1.1rem;
  margin-bottom: 16px;
}

.hero-stats {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 8px;
  color: var(--text-muted);
  font-size: 0.9rem;
}

.stats-dot {
  opacity: 0.4;
}

/* ===== Filters ===== */
.filters {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 24px 24px;
}

.search-box {
  position: relative;
}

.search-icon {
  position: absolute;
  left: 16px;
  top: 50%;
  transform: translateY(-50%);
  font-size: 0.95rem;
  color: var(--text-muted);
  pointer-events: none;
}

.search-box input {
  width: 100%;
  padding: 12px 18px 12px 44px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: var(--text);
  font-size: 1rem;
  outline: none;
  transition: border-color 0.2s;
}

.search-box input::placeholder {
  color: var(--text-muted);
}

.search-box input:focus {
  border-color: var(--accent);
}

.tag-filters {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 16px;
}

.tag-filter-btn {
  padding: 5px 14px;
  border-radius: 20px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text-muted);
  font-size: 0.8rem;
  cursor: pointer;
  transition: all 0.2s;
}

.tag-filter-btn:hover,
.tag-filter-btn.active {
  background: var(--tag-bg);
  color: var(--tag-text);
  border-color: var(--accent);
}

/* ===== Paper Grid — fixed 2 columns ===== */
.paper-grid {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 24px 60px;
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 24px;
}

.paper-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  transition: all 0.25s;
  cursor: pointer;
  display: flex;
  flex-direction: column;
}

.paper-card:hover {
  border-color: var(--accent);
  transform: translateY(-4px);
  box-shadow: 0 12px 40px rgba(108, 155, 255, 0.1);
}

@media (hover: none) {
  .paper-card:hover {
    transform: none;
    box-shadow: none;
  }

  .paper-card:active {
    border-color: var(--accent);
    background: var(--surface-hover);
  }
}

.paper-card .card-image {
  width: 100%;
  height: 200px;
  object-fit: cover;
  display: block;
  border-bottom: 1px solid var(--border);
}

.paper-card .card-image-placeholder {
  width: 100%;
  height: 200px;
  background: linear-gradient(135deg, #1e2a3a 0%, #2a1e3a 100%);
  display: flex;
  align-items: center;
  justify-content: center;
  border-bottom: 1px solid var(--border);
}

.paper-card .card-image-placeholder span {
  font-size: 3rem;
  color: var(--accent);
  opacity: 0.3;
}

.paper-card .card-body {
  padding: 20px;
  display: flex;
  flex-direction: column;
  flex: 1;
}

.paper-card .date {
  font-size: 0.78rem;
  color: var(--text-muted);
  margin-bottom: 8px;
}

.paper-card h3 {
  font-size: 1.05rem;
  font-weight: 600;
  margin-bottom: 10px;
  line-height: 1.4;
}

.paper-card .authors {
  font-size: 0.82rem;
  color: var(--text-muted);
  margin-bottom: 12px;
}

.paper-card .tags {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: auto;
}

.tag {
  background: var(--tag-bg);
  color: var(--tag-text);
  padding: 3px 10px;
  border-radius: 12px;
  font-size: 0.75rem;
}

/* ===== Paper Detail ===== */
.paper-detail {
  max-width: 800px;
  margin: 0 auto;
  padding: 48px 24px 80px;
}

.paper-detail .back-link {
  display: inline-block;
  margin-bottom: 32px;
  color: var(--text-muted);
  font-size: 0.9rem;
}

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

.paper-detail .meta {
  margin-bottom: 32px;
}

.paper-detail .meta .date {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: 8px;
}

.paper-detail .meta h1 {
  font-size: 2rem;
  font-weight: 800;
  letter-spacing: -0.5px;
  line-height: 1.3;
  margin-bottom: 8px;
}

.paper-detail .meta .authors {
  color: var(--text-muted);
  font-size: 0.95rem;
  margin-bottom: 12px;
}

.paper-detail .meta .paper-link {
  display: inline-block;
  margin-bottom: 12px;
  font-size: 0.9rem;
}

.paper-detail .meta .tags {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.paper-detail .review-content h2 {
  font-size: 1.4rem;
  font-weight: 700;
  margin: 36px 0 16px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border);
}

.paper-detail .review-content h3 {
  font-size: 1.15rem;
  font-weight: 600;
  margin: 24px 0 12px;
}

.paper-detail .review-content p {
  margin-bottom: 16px;
  line-height: 1.8;
}

.paper-detail .review-content ul,
.paper-detail .review-content ol {
  margin-bottom: 16px;
  padding-left: 24px;
}

.paper-detail .review-content li {
  margin-bottom: 6px;
  line-height: 1.7;
}

.paper-detail .review-content code {
  background: var(--surface);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.9em;
}

.paper-detail .review-content pre {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  overflow-x: auto;
  margin-bottom: 16px;
}

.paper-detail .review-content pre code {
  background: none;
  padding: 0;
}

.paper-detail .review-content table {
  width: 100%;
  border-collapse: collapse;
  margin: 16px 0 24px;
  font-size: 0.9rem;
}

.paper-detail .review-content th,
.paper-detail .review-content td {
  padding: 10px 14px;
  border: 1px solid var(--border);
  text-align: left;
  line-height: 1.5;
}

.paper-detail .review-content th {
  background: var(--surface);
  font-weight: 600;
  color: var(--text);
}

.paper-detail .review-content td {
  color: var(--text-muted);
}

.paper-detail .review-content tr:hover td {
  background: var(--surface);
}

.paper-detail .review-content blockquote {
  border-left: 3px solid var(--accent);
  padding: 12px 20px;
  margin: 16px 0;
  background: var(--surface);
  border-radius: 0 var(--radius) var(--radius) 0;
  color: var(--text-muted);
}

.paper-detail .review-content img {
  max-width: 100%;
  border-radius: var(--radius);
  display: block;
}

.paper-detail .review-content figure {
  margin: 24px 0;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
}

.paper-detail .review-content figure img {
  width: 100%;
  border-radius: 0;
  display: block;
}

.paper-detail .review-content figcaption {
  padding: 12px 16px;
  font-size: 0.85rem;
  color: var(--text-muted);
  text-align: center;
  border-top: 1px solid var(--border);
}

/* ===== Empty State ===== */
.empty-state {
  text-align: center;
  padding: 80px 24px;
  color: var(--text-muted);
  grid-column: 1 / -1;
}

.empty-state p {
  font-size: 1.1rem;
}

/* ===== Footer ===== */
footer {
  margin-top: auto;
  border-top: 1px solid var(--border);
  background: var(--surface);
}

.footer-inner {
  max-width: 1100px;
  margin: 0 auto;
  padding: 40px 24px 32px;
  text-align: center;
}

.footer-brand {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 8px;
}

.footer-desc {
  color: var(--text-muted);
  font-size: 0.9rem;
  margin-bottom: 24px;
}

.footer-links {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 20px;
}

.footer-icon-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 6px;
  text-decoration: none;
}

.footer-icon-item:hover .footer-icon-circle {
  color: var(--accent);
  border-color: var(--accent);
  background: var(--tag-bg);
  transform: translateY(-2px);
}

.footer-icon-item:hover .footer-icon-label {
  color: var(--accent);
}

.footer-icon-circle {
  width: 42px;
  height: 42px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: var(--bg);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-muted);
  transition: all 0.2s;
}

.footer-icon-circle svg {
  width: 18px;
  height: 18px;
}

.footer-icon-label {
  font-size: 0.7rem;
  color: var(--text-muted);
  transition: color 0.2s;
}

/* ===== Responsive — Tablet ===== */
@media (max-width: 900px) {
  .paper-grid {
    grid-template-columns: 1fr;
    max-width: 600px;
  }

  .paper-card .card-image,
  .paper-card .card-image-placeholder {
    height: 180px;
  }
}

/* ===== Responsive — Mobile ===== */
@media (max-width: 600px) {
  /* Header */
  .header-inner {
    padding: 12px 16px;
  }

  .logo {
    font-size: 1.05rem;
  }

  .logo-icon {
    font-size: 1.2rem;
  }

  .header-nav .nav-link {
    display: none;
  }

  .lang-btn {
    padding: 5px 10px;
    font-size: 0.8rem;
  }

  /* Hero */
  .hero {
    padding: 40px 16px 24px;
  }

  .hero h1 {
    font-size: 1.6rem;
    letter-spacing: -0.5px;
  }

  .hero p {
    font-size: 0.95rem;
  }

  .hero-stats {
    font-size: 0.8rem;
  }

  /* Filters */
  .filters {
    padding: 0 16px 16px;
  }

  .search-box input {
    padding: 10px 14px 10px 40px;
    font-size: 0.9rem;
  }

  .search-icon {
    left: 14px;
    font-size: 0.85rem;
  }

  .tag-filters {
    gap: 6px;
    margin-top: 12px;
  }

  .tag-filter-btn {
    padding: 4px 10px;
    font-size: 0.72rem;
  }

  /* Paper Grid */
  .paper-grid {
    grid-template-columns: 1fr;
    padding: 0 16px 40px;
    gap: 16px;
  }

  .paper-card .card-image,
  .paper-card .card-image-placeholder {
    height: 160px;
  }

  .paper-card .card-body {
    padding: 16px;
  }

  .paper-card h3 {
    font-size: 0.95rem;
  }

  .paper-card .authors {
    font-size: 0.78rem;
  }

  .paper-card .date {
    font-size: 0.72rem;
  }

  .tag {
    font-size: 0.68rem;
    padding: 2px 8px;
  }

  /* Paper Detail */
  .paper-detail {
    padding: 32px 16px 60px;
  }

  .paper-detail .back-link {
    margin-bottom: 20px;
    font-size: 0.85rem;
  }

  .paper-detail .meta h1 {
    font-size: 1.35rem;
    line-height: 1.4;
  }

  .paper-detail .meta .authors {
    font-size: 0.85rem;
  }

  .paper-detail .meta .paper-link {
    font-size: 0.85rem;
  }

  .paper-detail .review-content h2 {
    font-size: 1.15rem;
    margin: 28px 0 12px;
  }

  .paper-detail .review-content h3 {
    font-size: 1rem;
  }

  .paper-detail .review-content p {
    font-size: 0.9rem;
    line-height: 1.7;
  }

  .paper-detail .review-content li {
    font-size: 0.9rem;
    line-height: 1.6;
  }

  .paper-detail .review-content blockquote {
    padding: 10px 14px;
    font-size: 0.9rem;
  }

  /* Tables — horizontal scroll on mobile */
  .paper-detail .review-content table {
    display: block;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
    font-size: 0.8rem;
  }

  .paper-detail .review-content th,
  .paper-detail .review-content td {
    padding: 8px 10px;
    white-space: nowrap;
  }

  .paper-detail .review-content figure {
    margin: 16px -16px;
    border-radius: 0;
    border-left: none;
    border-right: none;
  }

  .paper-detail .review-content figcaption {
    padding: 10px 16px;
    font-size: 0.78rem;
  }

  /* Footer */
  .footer-inner {
    padding: 32px 16px 24px;
  }

  .footer-brand {
    font-size: 1rem;
  }

  .footer-desc {
    font-size: 0.82rem;
    margin-bottom: 20px;
  }

  .footer-links {
    gap: 14px;
  }

  .footer-icon-circle {
    width: 36px;
    height: 36px;
  }

  .footer-icon-circle svg {
    width: 15px;
    height: 15px;
  }

  .footer-icon-label {
    font-size: 0.62rem;
  }

  /* Empty state */
  .empty-state {
    padding: 48px 16px;
  }
}

/* ===== Responsive — Small phones ===== */
@media (max-width: 380px) {
  .hero h1 {
    font-size: 1.35rem;
  }

  .hero p {
    font-size: 0.88rem;
  }

  .paper-detail .meta h1 {
    font-size: 1.2rem;
  }

  .footer-links {
    gap: 10px;
  }

  .footer-icon-circle {
    width: 32px;
    height: 32px;
  }

  .footer-icon-circle svg {
    width: 13px;
    height: 13px;
  }
}