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

:root {
  --bg: #0f172a;
  --bg-card: #1e293b;
  --bg-hover: #334155;
  --text: #e2e8f0;
  --text-muted: #94a3b8;
  --accent: #38bdf8;
  --accent-glow: rgba(56, 189, 248, 0.15);
  --again: #ef4444;
  --hard: #f97316;
  --good: #22c55e;
  --easy: #3b82f6;
  --border: rgba(255,255,255,0.06);
  --radius: 16px;
}

body {
  font-family: "PingFang SC", "Microsoft YaHei", "Noto Sans SC", sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  line-height: 1.6;
}

/* Header */
.header {
  padding: 24px 32px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 16px;
  border-bottom: 1px solid var(--border);
  background: rgba(15, 23, 42, 0.8);
  backdrop-filter: blur(12px);
  position: sticky;
  top: 0;
  z-index: 100;
}

.header h1 {
  font-size: 22px;
  font-weight: 700;
  background: linear-gradient(135deg, var(--accent), #a78bfa);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  display: flex;
  align-items: center;
  gap: 10px;
}

.header h1::before {
  content: "";
  display: inline-block;
  width: 28px;
  height: 28px;
  background: linear-gradient(135deg, var(--accent), #a78bfa);
  border-radius: 8px;
  transform: rotate(-12deg);
}

.header-actions {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.btn {
  padding: 8px 18px;
  border: 1px solid var(--border);
  background: var(--bg-card);
  color: var(--text);
  border-radius: 10px;
  cursor: pointer;
  font-size: 13px;
  font-weight: 500;
  transition: all 0.2s;
  display: flex;
  align-items: center;
  gap: 6px;
}

.btn:hover {
  background: var(--bg-hover);
  border-color: var(--accent);
  box-shadow: 0 0 20px var(--accent-glow);
}

.btn-primary {
  background: linear-gradient(135deg, var(--accent), #6366f1);
  border: none;
  color: #fff;
}

.btn-primary:hover {
  opacity: 0.9;
  box-shadow: 0 0 30px rgba(56, 189, 248, 0.3);
}

/* Drop Zone */
.drop-zone {
  margin: 32px;
  padding: 60px 40px;
  border: 2px dashed rgba(56, 189, 248, 0.3);
  border-radius: var(--radius);
  text-align: center;
  transition: all 0.3s;
  background: rgba(30, 41, 59, 0.4);
}

.drop-zone.drag-over {
  border-color: var(--accent);
  background: var(--accent-glow);
  transform: scale(1.01);
}

.drop-zone.hidden { display: none; }

.drop-zone p {
  color: var(--text-muted);
  font-size: 15px;
  margin-top: 12px;
}

.drop-zone .icon {
  font-size: 48px;
  opacity: 0.6;
}

/* Stats Bar */
.stats-bar {
  display: flex;
  gap: 16px;
  padding: 0 32px 24px;
  flex-wrap: wrap;
}

.stat-card {
  flex: 1;
  min-width: 140px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 16px 20px;
}

.stat-card .label {
  font-size: 12px;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.stat-card .value {
  font-size: 28px;
  font-weight: 700;
  margin-top: 4px;
}

.stat-card .value.accent { color: var(--accent); }
.stat-card .value.green { color: var(--good); }
.stat-card .value.orange { color: var(--hard); }
.stat-card .value.red { color: var(--again); }

/* Filter Tabs */
.filter-tabs {
  display: flex;
  gap: 8px;
  padding: 0 32px 20px;
  flex-wrap: wrap;
}

.tab {
  padding: 6px 14px;
  border-radius: 20px;
  font-size: 13px;
  cursor: pointer;
  background: var(--bg-card);
  border: 1px solid var(--border);
  color: var(--text-muted);
  transition: all 0.2s;
}

.tab:hover, .tab.active {
  background: var(--accent-glow);
  border-color: var(--accent);
  color: var(--accent);
}

.tab .count {
  display: inline-block;
  margin-left: 6px;
  font-size: 11px;
  opacity: 0.7;
}

/* Card Grid */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 20px;
  padding: 0 32px 40px;
}

.card-container {
  perspective: 1200px;
  height: 220px;
  cursor: pointer;
}

.card {
  position: relative;
  width: 100%;
  height: 100%;
  transform-style: preserve-3d;
  transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
}

.card.flipped { transform: rotateY(180deg); }

.card-face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  border-radius: var(--radius);
  padding: 24px;
  display: flex;
  flex-direction: column;
  border: 1px solid var(--border);
  overflow: hidden;
}

.card-front {
  background: var(--bg-card);
}

.card-front::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--accent), #a78bfa);
  opacity: 0;
  transition: opacity 0.3s;
}

.card-container:hover .card-front::before { opacity: 1; }

.card-back {
  background: linear-gradient(135deg, #1e293b, #0f172a);
  transform: rotateY(180deg);
  overflow-y: auto;
  font-size: 13px;
  line-height: 1.7;
}

.card-back::-webkit-scrollbar { width: 4px; }
.card-back::-webkit-scrollbar-thumb { background: var(--bg-hover); border-radius: 2px; }

.card-title {
  font-size: 15px;
  font-weight: 600;
  margin-bottom: 8px;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.card-meta {
  font-size: 11px;
  color: var(--text-muted);
  margin-top: auto;
  display: flex;
  align-items: center;
  gap: 12px;
}

.card-meta .source {
  background: rgba(56, 189, 248, 0.1);
  color: var(--accent);
  padding: 2px 8px;
  border-radius: 4px;
  font-size: 10px;
}

.card-meta .interval {
  color: var(--text-muted);
}

.card-back .answer-content {
  flex: 1;
}

.card-back .answer-content p,
.card-back .answer-content li {
  margin-bottom: 6px;
}

.card-back .answer-content ul, .card-back .answer-content ol {
  padding-left: 18px;
}

.card-back .answer-content code {
  background: rgba(255,255,255,0.08);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 12px;
}

.card-back .answer-content pre {
  background: rgba(0,0,0,0.3);
  padding: 12px;
  border-radius: 8px;
  overflow-x: auto;
  margin: 8px 0;
}

.card-back .answer-content pre code {
  background: none;
  padding: 0;
}

.card-back .answer-content table {
  width: 100%;
  border-collapse: collapse;
  margin: 8px 0;
  font-size: 12px;
}

.card-back .answer-content th,
.card-back .answer-content td {
  border: 1px solid var(--border);
  padding: 6px 10px;
  text-align: left;
}

.card-back .answer-content th {
  background: rgba(255,255,255,0.05);
  font-weight: 600;
}

.card-back .answer-content blockquote {
  border-left: 3px solid var(--accent);
  padding-left: 12px;
  margin: 8px 0;
  color: var(--text-muted);
}

.card-back .answer-content img {
  max-width: 100%;
  border-radius: 8px;
  margin: 8px 0;
}

/* Rating Buttons */
.rating-bar {
  display: flex;
  gap: 6px;
  margin-top: 12px;
  padding-top: 12px;
  border-top: 1px solid var(--border);
}

.rating-btn {
  flex: 1;
  padding: 8px 4px;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  font-size: 11px;
  font-weight: 600;
  color: #fff;
  transition: all 0.2s;
  text-align: center;
}

.rating-btn:hover { transform: translateY(-2px); }

.rating-btn.again { background: var(--again); }
.rating-btn.hard { background: var(--hard); }
.rating-btn.good { background: var(--good); }
.rating-btn.easy { background: var(--easy); }

.rating-btn .interval {
  display: block;
  font-size: 10px;
  opacity: 0.8;
  margin-top: 2px;
  font-weight: 400;
}

/* Stats Modal */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.6);
  backdrop-filter: blur(4px);
  z-index: 200;
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.3s;
}

.modal-overlay.show {
  opacity: 1;
  pointer-events: auto;
}

.modal {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 32px;
  max-width: 500px;
  width: 90%;
  max-height: 80vh;
  overflow-y: auto;
  transform: translateY(20px);
  transition: transform 0.3s;
}

.modal-overlay.show .modal { transform: translateY(0); }

.modal h2 {
  font-size: 20px;
  margin-bottom: 24px;
  display: flex;
  align-items: center;
  gap: 10px;
}

.modal h2::before {
  content: "";
  display: inline-block;
  width: 20px;
  height: 20px;
  background: linear-gradient(135deg, var(--accent), #a78bfa);
  border-radius: 6px;
}

.chart-row {
  display: flex;
  gap: 20px;
  margin-bottom: 24px;
  flex-wrap: wrap;
}

.chart-box {
  flex: 1;
  min-width: 200px;
}

.chart-box h3 {
  font-size: 13px;
  color: var(--text-muted);
  margin-bottom: 12px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.pie-chart {
  width: 160px;
  height: 160px;
  border-radius: 50%;
  position: relative;
  margin: 0 auto;
}

.pie-chart::after {
  content: "";
  position: absolute;
  inset: 30px;
  background: var(--bg-card);
  border-radius: 50%;
}

.pie-legend {
  margin-top: 16px;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.legend-item {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
}

.legend-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  flex-shrink: 0;
}

.legend-item .pct {
  margin-left: auto;
  font-weight: 600;
  color: var(--accent);
}

.history-list {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.history-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 12px;
  background: rgba(255,255,255,0.03);
  border-radius: 8px;
  font-size: 13px;
}

.history-item .dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  flex-shrink: 0;
}

.history-item .time {
  color: var(--text-muted);
  font-size: 11px;
  margin-left: auto;
}

.close-modal {
  position: absolute;
  top: 16px;
  right: 16px;
  background: none;
  border: none;
  color: var(--text-muted);
  font-size: 20px;
  cursor: pointer;
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 8px;
  transition: all 0.2s;
}

.close-modal:hover {
  background: var(--bg-hover);
  color: var(--text);
}

.modal { position: relative; }

/* Empty State */
.empty-state {
  text-align: center;
  padding: 80px 20px;
  color: var(--text-muted);
}

.empty-state .icon { font-size: 64px; opacity: 0.4; margin-bottom: 16px; }
.empty-state p { font-size: 15px; }

/* Responsive */
@media (max-width: 640px) {
  .header { padding: 12px 16px; gap: 8px; }
  .header h1 { font-size: 16px; width: 100%; }
  .header-actions { width: 100%; justify-content: flex-start; flex-wrap: wrap; gap: 6px; }
  .header-actions .btn { padding: 6px 8px; font-size: 11px; flex: 1 1 auto; justify-content: center; min-width: 0; }
  
  .drop-zone { margin: 12px 0; padding: 20px 16px; }
  .drop-zone h2 { font-size: 15px; }
  .drop-zone p { font-size: 11px; }
  
  .stats-bar { padding: 0 0 10px; gap: 8px; flex-wrap: wrap; }
  .stat-card { flex: 1 1 calc(50% - 4px); padding: 8px 10px; }
  .stat-card .label { font-size: 9px; }
  .stat-card .value { font-size: 18px; }
  
  .search-box { padding: 0 0 10px; }
  .search-input { width: 100%; max-width: none; font-size: 14px; padding: 8px 12px; border-radius: 8px; box-sizing: border-box; }
  
  .file-list { padding: 0 0 12px; gap: 6px; flex-wrap: wrap; width: 100%; max-width: 100%; box-sizing: border-box; }
  .file-tags { flex: 1 1 100%; gap: 6px; display: flex; flex-wrap: wrap; }
  .file-tag { font-size: 11px; padding: 5px 10px; }
  .btn-delete-mode { padding: 5px 10px; font-size: 11px; }
  
  .file-selector { padding: 0 0 10px; }
  .file-select { width: 100%; font-size: 14px; padding: 8px; border-radius: 8px; }
  
  .filter-tabs { padding: 0 0 10px; gap: 6px; overflow-x: auto; flex-wrap: nowrap; }
  .tab { padding: 5px 10px; font-size: 11px; white-space: nowrap; }
  
  .card-grid { padding: 0 0 24px; grid-template-columns: 1fr; gap: 12px; }
  .card-container { height: 160px; }
  .card-face { padding: 14px; }
  .card-title { font-size: 13px; }
  .card-meta { font-size: 10px; }
  
  .modal { width: 95%; padding: 16px; max-height: 85vh; }
  .pie-chart { width: 100px; height: 100px; }
  .pie-chart::after { inset: 18px; }
  
  .rating-bar { gap: 4px; }
  .rating-btn { padding: 8px 4px; font-size: 10px; }
  
  .study-view { padding: 10px; }
  .study-header { padding: 12px; gap: 8px; }
  .study-progress { font-size: 14px; }
  .study-card { padding: 14px; min-height: 280px; }
  .study-card-title { font-size: 16px; }
  .study-card-content { font-size: 13px; }
  .study-nav { flex-direction: column; gap: 8px; padding: 10px; }
  .nav-btn { width: 100%; font-size: 12px; padding: 10px; }
  .swipe-hint { display: none; }
}

/* Animations */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: translateY(0); }
}

.card-container { animation: fadeIn 0.4s ease backwards; }
.card-container:nth-child(1) { animation-delay: 0.05s; }
.card-container:nth-child(2) { animation-delay: 0.1s; }
.card-container:nth-child(3) { animation-delay: 0.15s; }
.card-container:nth-child(4) { animation-delay: 0.2s; }
.card-container:nth-child(5) { animation-delay: 0.25s; }
.card-container:nth-child(6) { animation-delay: 0.3s; }
.card-container:nth-child(n+7) { animation-delay: 0.35s; }

.hidden { display: none !important; }

/* File list */
.file-list {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 0 32px 16px;
  flex-wrap: wrap;
}

.file-tags {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  flex: 1;
  min-width: 0;
}

.file-tag {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px 14px;
  background: rgba(56, 189, 248, 0.08);
  border: 1px solid rgba(56, 189, 248, 0.2);
  border-radius: 20px;
  font-size: 12px;
  color: var(--accent);
  cursor: pointer;
  transition: all 0.2s;
  white-space: nowrap;
}

.file-tag:hover {
  background: rgba(56, 189, 248, 0.15);
}

.file-tag.active {
  background: rgba(56, 189, 248, 0.2);
  border-color: var(--accent);
}

.file-tag.delete-mode {
  background: rgba(239, 68, 68, 0.1);
  border-color: var(--again);
  color: var(--again);
}

.file-tag.delete-mode:hover {
  background: rgba(239, 68, 68, 0.25);
}

.btn-delete-mode {
  padding: 6px 14px;
  font-size: 12px;
  flex-shrink: 0;
}

.btn-delete-mode.active {
  background: var(--again);
  border-color: var(--again);
  color: #fff;
}

/* File Selector */
.file-selector {
  padding: 0 32px 16px;
  display: none;
}
.file-selector.show { display: block; }
.file-select {
  padding: 8px 14px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 10px;
  color: var(--text);
  font-size: 13px;
  outline: none;
  cursor: pointer;
  min-width: 200px;
}
.file-select:focus { border-color: var(--accent); }
.file-select option { background: var(--bg-card); }

/* Search */
.search-box {
  padding: 0 32px 16px;
}

.search-input {
  width: 100%;
  max-width: 400px;
  padding: 10px 16px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 10px;
  color: var(--text);
  font-size: 14px;
  outline: none;
  transition: all 0.2s;
}

.search-input::placeholder { color: var(--text-muted); }
.search-input:focus { border-color: var(--accent); box-shadow: 0 0 20px var(--accent-glow); }

/* Study Mode */
.study-view {
  position: fixed;
  inset: 0;
  background: var(--bg);
  z-index: 300;
  display: flex;
  flex-direction: column;
  padding: 20px;
  overflow-x: hidden;
}

.study-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px;
  border-bottom: 1px solid var(--border);
}

.study-progress {
  font-size: 16px;
  font-weight: 600;
  color: var(--accent);
}

.study-card-container {
  flex: 1;
  display: flex;
  justify-content: center;
  padding: 20px;
  overflow: hidden;
  user-select: none;
}

.study-card {
  width: 100%;
  max-width: 600px;
  min-height: 400px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 32px;
  display: flex;
  flex-direction: column;
  cursor: pointer;
  transition: transform 0.3s ease;
  overflow-x: hidden;
}

.study-card:hover {
  border-color: var(--accent);
  box-shadow: 0 0 30px var(--accent-glow);
}

.study-card.swiping {
  transition: none;
}

.study-card-front {
  flex: 1;
  display: flex;
  flex-direction: column;
}

.study-card-back {
  display: none;
  flex-direction: column;
  flex: 1;
  overflow-y: auto;
}

.study-card.flipped .study-card-front {
  display: none;
}

.study-card.flipped .study-card-back {
  display: flex;
}

.study-card-title {
  font-size: 24px;
  font-weight: 700;
  margin-bottom: 16px;
  line-height: 1.4;
}

.study-card-meta {
  font-size: 13px;
  color: var(--text-muted);
  margin-top: auto;
  display: flex;
  align-items: center;
  gap: 12px;
}

.study-card-meta .source {
  background: rgba(56, 189, 248, 0.1);
  color: var(--accent);
  padding: 4px 10px;
  border-radius: 6px;
}

.study-card-content {
  flex: 1;
  font-size: 15px;
  line-height: 1.7;
  overflow-y: auto;
  overflow-x: hidden;
  margin-bottom: 16px;
}

.study-card-content img {
  max-width: 100%;
  height: auto;
}

.study-card-content p,
.study-card-content li { margin-bottom: 8px; }

.study-card-content ul,
.study-card-content ol { padding-left: 20px; }

.study-card-content code {
  background: rgba(255,255,255,0.1);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 13px;
}

.study-card-content pre {
  background: rgba(0,0,0,0.3);
  padding: 12px;
  border-radius: 8px;
  overflow-x: auto;
  margin: 8px 0;
}

.study-nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px;
  border-top: 1px solid var(--border);
}

.nav-btn {
  padding: 12px 20px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 10px;
  color: var(--text);
  font-size: 14px;
  cursor: pointer;
  transition: all 0.2s;
}

.nav-btn:hover {
  border-color: var(--accent);
  background: var(--bg-hover);
}

.nav-btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.swipe-hint {
  color: var(--text-muted);
  font-size: 12px;
}

.study-complete {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
}

.study-complete .icon {
  font-size: 64px;
  margin-bottom: 16px;
}

.study-complete h2 {
  font-size: 24px;
  margin-bottom: 12px;
  color: var(--good);
}

.study-complete p {
  color: var(--text-muted);
  margin-bottom: 24px;
}