/* CSS Variables */
:root {
  --bg-primary: #ffffff;
  --bg-secondary: #f8fafc;
  --bg-card: #ffffff;
  --bg-sidebar: #f8fafc;
  --text-primary: #0f172a;
  --text-secondary: #334155;
  --text-muted: #64748b;
  --border-color: #e2e8f0;
  --border-focus: #3b82f6;
  --accent-color: #2563eb;
  --accent-light: #eff6ff;
  --accent-hover: #1d4ed8;
  --success-color: #16a34a;
  --success-light: #f0fdf4;
  --danger-color: #dc2626;
  --danger-light: #fef2f2;
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --header-height: 52px;
  --sidebar-width: 250px;
}

body.theme-dark {
  --bg-primary: #0b0f19;
  --bg-secondary: #111827;
  --bg-card: #162032;
  --bg-sidebar: #0f172a;
  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  --border-color: #223048;
  --border-focus: #60a5fa;
  --accent-color: #3b82f6;
  --accent-light: #1e3a8a33;
  --accent-hover: #60a5fa;
  --success-color: #22c55e;
  --success-light: #052e1633;
  --danger-color: #ef4444;
  --danger-light: #450a0a33;
}

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

html, body {
  height: 100%;
  font-family: var(--font-sans);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

#app {
  display: flex;
  flex-direction: column;
  height: 100vh;
  overflow: hidden;
}

/* Navbar */
.navbar {
  height: var(--header-height);
  background-color: var(--bg-primary);
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 16px;
  z-index: 100;
  flex-shrink: 0;
}

.nav-left, .nav-right {
  display: flex;
  align-items: center;
  gap: 8px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 6px;
  cursor: pointer;
  user-select: none;
  white-space: nowrap;
}
.brand-logo { font-size: 18px; }
.brand-title {
  font-size: 15px;
  font-weight: 700;
  letter-spacing: -0.3px;
  white-space: nowrap;
}
.brand-badge {
  font-size: 11px;
  font-weight: 600;
  padding: 2px 6px;
  background-color: var(--accent-light);
  color: var(--accent-color);
  border-radius: 9999px;
  white-space: nowrap;
}

/* Mode Tabs (Desktop) */
.mode-tabs {
  display: flex;
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  padding: 3px;
  gap: 3px;
}

.mode-tab {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 6px 16px;
  font-size: 13px;
  font-weight: 600;
  color: var(--text-secondary);
  background: transparent;
  border: none;
  border-radius: 6px;
  cursor: pointer;
  transition: all 0.15s ease;
  white-space: nowrap;
}

.mode-tab:hover {
  color: var(--text-primary);
}

.mode-tab.active {
  background-color: var(--bg-card);
  color: var(--accent-color);
  box-shadow: 0 1px 3px rgba(0,0,0,0.08);
}

/* Mobile Sub-Header (Full Width Segment Control) */
.mobile-subnav {
  padding: 8px 12px;
  background-color: var(--bg-primary);
  border-bottom: 1px solid var(--border-color);
  flex-shrink: 0;
  z-index: 90;
}
.mobile-tabs {
  width: 100%;
}
.mobile-tabs .mode-tab {
  flex: 1;
  padding: 8px 10px;
}

.desktop-only { display: flex; }
.mobile-only { display: none; }

/* Buttons & Controls */
.btn-icon {
  background: transparent;
  border: 1px solid transparent;
  color: var(--text-secondary);
  width: 34px;
  height: 34px;
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all 0.15s;
}
.btn-icon:hover {
  background-color: var(--bg-secondary);
  color: var(--text-primary);
}

.btn-action {
  display: flex;
  align-items: center;
  gap: 6px;
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  padding: 5px 12px;
  border-radius: 6px;
  font-size: 13px;
  cursor: pointer;
  transition: all 0.15s;
}
.btn-action:hover {
  border-color: var(--accent-color);
  color: var(--accent-color);
}
.btn-action kbd {
  background-color: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: 4px;
  font-size: 10px;
  padding: 1px 5px;
}

/* Theme Icons */
.theme-icon { display: none; }
body.theme-system .icon-system { display: block; }
body.theme-light .icon-light { display: block; }
body.theme-dark .icon-dark { display: block; }

/* Layout Container */
.layout-container {
  display: flex;
  flex: 1;
  overflow: hidden;
  position: relative;
}

/* Sidebar */
.sidebar {
  width: var(--sidebar-width);
  background-color: var(--bg-sidebar);
  border-right: 1px solid var(--border-color);
  display: flex;
  flex-direction: column;
  flex-shrink: 0;
  transition: transform 0.25s ease;
  z-index: 50;
}

.sidebar.hidden {
  transform: translateX(-100%);
  margin-right: calc(-1 * var(--sidebar-width));
}

.sidebar-header {
  padding: 14px 16px;
  border-bottom: 1px solid var(--border-color);
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 13px;
  font-weight: 700;
  color: var(--text-secondary);
}
.sidebar-count {
  font-size: 11px;
  color: var(--text-muted);
}

.sidebar-scroll {
  flex: 1;
  overflow-y: auto;
  padding: 10px 8px;
}

.period-group {
  margin-bottom: 14px;
}
.period-title {
  font-size: 11px;
  font-weight: 700;
  color: var(--text-muted);
  padding: 4px 8px 6px;
  letter-spacing: 0.3px;
}

.year-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 8px 10px;
  margin-bottom: 2px;
  border-radius: 6px;
  font-size: 13px;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.15s;
}
.year-item:hover {
  background-color: rgba(0,0,0,0.04);
  color: var(--text-primary);
}
body.theme-dark .year-item:hover {
  background-color: rgba(255,255,255,0.05);
}
.year-item.active {
  background-color: var(--accent-light);
  color: var(--accent-color);
  font-weight: 700;
}

.item-badge {
  font-size: 10px;
  padding: 1px 5px;
  border-radius: 4px;
  background-color: var(--border-color);
  color: var(--text-muted);
}
.year-item.active .item-badge {
  background-color: var(--accent-color);
  color: #fff;
}

/* Main Content Area */
.main-content {
  flex: 1;
  overflow-y: auto;
  position: relative;
  background-color: var(--bg-primary);
  scroll-behavior: smooth;
}

.content-wrapper {
  max-width: 880px;
  margin: 0 auto;
  padding: 20px 20px 100px;
}

/* Compact Banner */
.paper-banner {
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  padding: 16px 18px;
  margin-bottom: 24px;
}

.banner-top-row {
  margin-bottom: 12px;
}
.banner-top-row h1 {
  font-size: 19px;
  font-weight: 800;
  letter-spacing: -0.3px;
  margin-bottom: 8px;
}

.banner-badges {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}
.badge {
  font-size: 11px;
  padding: 2px 8px;
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: 4px;
  color: var(--text-secondary);
}
.badge-accent {
  background-color: var(--accent-light);
  border-color: transparent;
  color: var(--accent-color);
  font-weight: 600;
}

.banner-controls {
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-top: 1px solid var(--border-color);
  padding-top: 10px;
}

.btn-text {
  background: transparent;
  border: none;
  font-size: 13px;
  font-weight: 600;
  color: var(--accent-color);
  cursor: pointer;
  padding: 4px 6px;
  border-radius: 4px;
}
.btn-text:disabled {
  opacity: 0.3;
  cursor: not-allowed;
}

.quick-year-select select {
  font-size: 13px;
  padding: 4px 10px;
  border-radius: 6px;
  border: 1px solid var(--border-color);
  background-color: var(--bg-card);
  color: var(--text-primary);
}

/* Section Container & Titles */
.section-block {
  margin-bottom: 32px;
}

.sec-title-bar {
  margin: 28px 0 14px;
  padding-bottom: 8px;
  border-bottom: 2px solid var(--border-color);
}
.sec-title-text {
  font-size: 18px;
  font-weight: 800;
  color: var(--accent-color);
}
.sec-desc-text {
  font-size: 13px;
  color: var(--text-muted);
  margin-top: 4px;
}

/* Question Card */
.question-card {
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  padding: 18px 20px;
  margin-bottom: 20px;
  transition: all 0.2s ease;
  scroll-margin-top: 70px;
}

.question-card:hover {
  border-color: #cbd5e1;
  box-shadow: 0 2px 8px rgba(0,0,0,0.04);
}
body.theme-dark .question-card:hover {
  border-color: #334155;
  box-shadow: 0 2px 8px rgba(0,0,0,0.3);
}

/* Question Header */
.q-card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 12px;
}
.q-num-pill {
  font-size: 13px;
  font-weight: 800;
  color: var(--accent-color);
  background-color: var(--accent-light);
  padding: 2px 8px;
  border-radius: 4px;
}

/* Question Body */
.q-card-body {
  font-size: 15px;
  line-height: 1.8;
  color: var(--text-primary);
  margin-bottom: 14px;
}
.q-card-body p { margin-bottom: 10px; }
.q-card-body p:last-child { margin-bottom: 0; }

/* Interactive Options Container */
.options-container {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin: 14px 0 16px;
}

.option-card {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding: 10px 14px;
  background-color: var(--bg-secondary);
  border: 1.5px solid var(--border-color);
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.15s ease;
  user-select: none;
}

.option-card:hover {
  border-color: var(--border-focus);
}

.option-card.selected {
  border-color: var(--accent-color);
  background-color: var(--accent-light);
  box-shadow: 0 0 0 1px var(--accent-color);
}

.option-card.correct-highlight {
  border-color: var(--success-color) !important;
  background-color: var(--success-light) !important;
  box-shadow: 0 0 0 1px var(--success-color);
}

.option-card.wrong-highlight {
  border-color: var(--danger-color) !important;
  background-color: var(--danger-light) !important;
}

.opt-badge {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  font-size: 12px;
  font-weight: 700;
  color: var(--text-secondary);
  flex-shrink: 0;
  margin-top: 1px;
}

.option-card.selected .opt-badge {
  background-color: var(--accent-color);
  border-color: var(--accent-color);
  color: #fff;
}

.option-card.correct-highlight .opt-badge {
  background-color: var(--success-color) !important;
  border-color: var(--success-color) !important;
  color: #fff !important;
}

.option-card.wrong-highlight .opt-badge {
  background-color: var(--danger-color) !important;
  border-color: var(--danger-color) !important;
  color: #fff !important;
}

.opt-content {
  flex: 1;
  font-size: 14.5px;
  line-height: 1.6;
}

.sol-tag-correct {
  display: inline-block;
  font-size: 11px;
  font-weight: 700;
  color: var(--success-color);
  background-color: var(--success-light);
  padding: 1px 6px;
  border-radius: 4px;
  margin-left: 8px;
}

/* Action Bar under question */
.q-action-bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin-top: 12px;
  padding-top: 10px;
  border-top: 1px dashed var(--border-color);
}

.btn-pill {
  padding: 4px 12px;
  font-size: 12px;
  font-weight: 600;
  border-radius: 6px;
  cursor: pointer;
  border: 1px solid var(--border-color);
  background-color: var(--bg-card);
  color: var(--text-secondary);
  transition: all 0.15s;
}
.btn-pill:hover {
  border-color: var(--accent-color);
  color: var(--accent-color);
}
.btn-pill.primary {
  background-color: var(--accent-color);
  color: #fff;
  border-color: transparent;
}
.btn-pill.primary:hover {
  background-color: var(--accent-hover);
}

.feedback-badge {
  font-size: 12px;
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: 4px;
}
.feedback-badge.correct { color: var(--success-color); }
.feedback-badge.wrong { color: var(--danger-color); }

/* Collapsible Solution Box */
.inline-solution-box {
  margin-top: 12px;
  padding: 14px;
  background-color: var(--bg-secondary);
  border-left: 3px solid var(--accent-color);
  border-radius: 0 8px 8px 0;
  display: none;
  font-size: 14.5px;
  line-height: 1.7;
}
.inline-solution-box.open {
  display: block;
}

/* Solution Mode Card Content */
.sol-view-box {
  margin-top: 14px;
  padding: 14px 16px;
  background-color: var(--bg-secondary);
  border-radius: 8px;
  font-size: 14.5px;
  line-height: 1.75;
}
.sol-ans-title {
  font-size: 13px;
  font-weight: 700;
  color: var(--success-color);
  margin-bottom: 6px;
}
.sol-body-content {
  color: var(--text-primary);
}

/* KaTeX Formula Display */
.katex-display {
  overflow-x: auto;
  overflow-y: hidden;
  padding: 8px 0;
  -webkit-overflow-scrolling: touch;
}
.katex {
  font-size: 1.05em !important;
}

/* Image centering */
.question-card img {
  max-width: 100%;
  height: auto;
  border-radius: 6px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.08);
  margin: 12px auto;
  display: block;
}

/* Search Jump Highlight Pulse Animation */
@keyframes targetPulse {
  0% { box-shadow: 0 0 0 0 rgba(37, 99, 235, 0.7); background-color: rgba(37, 99, 235, 0.12); }
  50% { box-shadow: 0 0 0 10px rgba(37, 99, 235, 0); background-color: rgba(37, 99, 235, 0.08); }
  100% { box-shadow: 0 0 0 0 rgba(37, 99, 235, 0); }
}
.highlight-target {
  animation: targetPulse 1.8s ease-out;
  border-color: var(--accent-color) !important;
}

/* Floating Quiz Bar */
.quiz-bar {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  background-color: var(--bg-card);
  border-top: 1px solid var(--border-color);
  padding: 10px 20px;
  box-shadow: 0 -4px 16px rgba(0,0,0,0.08);
  z-index: 95;
  display: flex;
  justify-content: center;
}
.quiz-bar.hidden { display: none; }

.quiz-bar-content {
  width: 100%;
  max-width: 880px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.quiz-info {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  font-weight: 600;
}
.quiz-score-badge {
  font-size: 12px;
  padding: 2px 6px;
  border-radius: 4px;
  background-color: var(--accent-light);
  color: var(--accent-color);
}

.quiz-actions {
  display: flex;
  gap: 8px;
}
.btn-quiz-primary {
  padding: 6px 14px;
  background-color: var(--accent-color);
  color: #fff;
  border: none;
  border-radius: 6px;
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
}
.btn-quiz-secondary {
  padding: 6px 10px;
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  border-radius: 6px;
  font-size: 13px;
  cursor: pointer;
}

/* Back to top */
.btn-back-top {
  position: fixed;
  bottom: 64px;
  right: 20px;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  box-shadow: 0 4px 12px rgba(0,0,0,0.1);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transition: all 0.2s ease;
  z-index: 80;
}
.btn-back-top.visible {
  opacity: 1;
  visibility: visible;
}

/* Search Modal */
.modal-overlay {
  position: fixed;
  top: 0; left: 0; right: 0; bottom: 0;
  background-color: rgba(0,0,0,0.5);
  backdrop-filter: blur(4px);
  z-index: 200;
  display: flex;
  align-items: flex-start;
  justify-content: center;
  padding-top: 60px;
}
.modal-overlay.hidden { display: none; }

.modal-card {
  width: 90%;
  max-width: 680px;
  max-height: 82vh;
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: 12px;
  box-shadow: 0 20px 25px -5px rgba(0,0,0,0.25);
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.modal-header {
  display: flex;
  align-items: center;
  padding: 12px 16px;
  border-bottom: 1px solid var(--border-color);
  gap: 10px;
}
.search-input-wrap {
  display: flex;
  align-items: center;
  flex: 1;
  gap: 10px;
}
.search-input-wrap input {
  flex: 1;
  border: none;
  outline: none;
  font-size: 15px;
  background: transparent;
  color: var(--text-primary);
}

.modal-body {
  flex: 1;
  overflow-y: auto;
  padding: 16px;
}

.search-tip {
  text-align: center;
  color: var(--text-muted);
  font-size: 13px;
  padding: 40px 0;
}

.search-result-item {
  padding: 12px 14px;
  border-radius: 8px;
  border: 1px solid var(--border-color);
  margin-bottom: 8px;
  cursor: pointer;
  transition: all 0.15s;
}
.search-result-item:hover {
  background-color: var(--bg-secondary);
  border-color: var(--accent-color);
  transform: translateY(-1px);
}
.search-res-header {
  display: flex;
  justify-content: space-between;
  margin-bottom: 6px;
  font-size: 13px;
  font-weight: 700;
  color: var(--accent-color);
}
.search-res-snippet {
  font-size: 13px;
  color: var(--text-secondary);
  line-height: 1.5;
}
.search-res-snippet mark {
  background-color: #fef08a;
  color: #854d0e;
  padding: 0 2px;
  border-radius: 2px;
}

/* Mobile responsive rules */
@media (max-width: 768px) {
  .desktop-only { display: none; }
  .mobile-only { display: block; }

  .navbar {
    padding: 0 10px;
  }
  .brand-title {
    font-size: 14px;
  }
  .brand-badge {
    display: none;
  }

  .sidebar {
    position: absolute;
    top: 0; bottom: 0; left: 0;
    box-shadow: 4px 0 16px rgba(0,0,0,0.15);
  }
  .sidebar.hidden {
    transform: translateX(-100%);
    margin-right: 0;
  }
  .sidebar-overlay {
    position: absolute;
    top: 0; left: 0; right: 0; bottom: 0;
    background-color: rgba(0,0,0,0.4);
    z-index: 40;
    display: none;
  }
  .sidebar-overlay.active { display: block; }
  
  .content-wrapper {
    padding: 14px 12px 90px;
  }
  .paper-banner {
    padding: 12px 14px;
    margin-bottom: 16px;
  }
  .banner-top-row h1 {
    font-size: 16px;
  }
  .search-text { display: none; }
  .btn-action kbd { display: none; }
}

/* Print Only Section */
.print-header { display: none; }

/* Print Stylesheet */
@media print {
  @page {
    size: A4 portrait;
    margin: 15mm 15mm 15mm 15mm;
  }
  
  html, body {
    height: auto !important;
    overflow: visible !important;
    background: #fff !important;
    color: #000 !important;
    font-size: 11pt !important;
    line-height: 1.6 !important;
  }

  /* Must NOT hide #app */
  #app {
    display: block !important;
    height: auto !important;
    overflow: visible !important;
  }

  .layout-container {
    display: block !important;
    height: auto !important;
    overflow: visible !important;
  }

  .main-content {
    display: block !important;
    height: auto !important;
    overflow: visible !important;
  }

  .content-wrapper {
    max-width: 100% !important;
    padding: 0 !important;
    margin: 0 !important;
  }

  /* Hide web chrome only */
  .navbar, .mobile-subnav, .sidebar, .sidebar-overlay, .banner-controls, 
  .btn-back-top, #search-modal, .quiz-bar, .q-action-bar, .banner-badges,
  .quick-year-select, .btn-pill, .feedback-badge, .inline-solution-box,
  .paper-banner {
    display: none !important;
  }

  .print-header {
    display: block !important;
    text-align: center;
    border-bottom: 2px solid #000;
    padding-bottom: 10pt;
    margin-bottom: 16pt;
  }
  .print-exam-type {
    font-size: 12pt;
    font-weight: 700;
    margin-bottom: 4pt;
  }
  .print-title {
    font-size: 16pt;
    font-weight: 800;
    margin-bottom: 4pt;
  }
  .print-code {
    font-size: 10.5pt;
    margin-bottom: 8pt;
  }
  .print-meta-grid {
    display: flex;
    justify-content: space-between;
    font-size: 10pt;
    border-top: 1px solid #000;
    padding-top: 6pt;
  }

  .question-card {
    border: none !important;
    background: transparent !important;
    box-shadow: none !important;
    padding: 0 !important;
    margin-bottom: 14pt !important;
    page-break-inside: avoid !important;
    break-inside: avoid !important;
  }

  .q-num-pill {
    background: transparent !important;
    color: #000 !important;
    font-weight: 800 !important;
    font-size: 11pt !important;
    padding: 0 !important;
  }

  .sec-title-bar {
    border-bottom: 1.5pt solid #000 !important;
    margin: 16pt 0 10pt !important;
    page-break-after: avoid !important;
    break-after: avoid !important;
  }
  .sec-title-text {
    color: #000 !important;
    font-size: 13pt !important;
  }

  .option-card {
    border: none !important;
    background: transparent !important;
    box-shadow: none !important;
    padding: 1.5pt 0 !important;
  }
  .opt-badge {
    border: 1px solid #000 !important;
    color: #000 !important;
    background: transparent !important;
  }

  .options-container, .question-card img {
    page-break-inside: avoid !important;
    break-inside: avoid !important;
  }
}