:root {
  --bg-page: #F8FAFC;
  --card-bg: #FFFFFF;
  --card-border: #E2E8F0;
  --card-hover-border: #CBD5E1;
  
  --text-primary: #0F172A;
  --text-secondary: #475569;
  --text-muted: #64748B;
  
  --primary: #2563EB;
  --primary-hover: #1D4ED8;
  
  /* Solution button: clean, crisp red without eye-straining glow */
  --btn-sol: #DC2626;
  --btn-sol-hover: #B91C1C;
  
  --diff-high-bg: #FEE2E2;
  --diff-high-text: #991B1B;
  --diff-mid-bg: #FEF3C7;
  --diff-mid-text: #92400E;
  --diff-low-bg: #DCFCE7;
  --diff-low-text: #166534;
  
  --font-family: 'Pretendard', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --radius-md: 10px;
  --radius-sm: 6px;
}

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

body {
  font-family: var(--font-family);
  background-color: var(--bg-page);
  color: var(--text-primary);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  padding-bottom: 50px;
}

.app-container {
  max-width: 1040px;
  margin: 0 auto;
  padding: 20px 16px;
}

/* ==================== NAVBAR ==================== */
.navbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 16px 22px;
  background: linear-gradient(135deg, #1E293B 0%, #0F172A 100%);
  border: 1px solid #334155;
  border-radius: var(--radius-md);
  margin-bottom: 20px;
  box-shadow: 0 4px 14px -1px rgba(15, 23, 42, 0.16), 0 2px 5px -1px rgba(15, 23, 42, 0.08);
}

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
}

.logo-badge {
  background: linear-gradient(135deg, #3B82F6 0%, #1D4ED8 100%);
  color: #FFFFFF;
  font-size: 12px;
  font-weight: 700;
  padding: 5px 10px;
  border-radius: 6px;
  letter-spacing: -0.2px;
  box-shadow: 0 2px 6px rgba(37, 99, 235, 0.35);
}

.brand-text h1 {
  font-size: 18px;
  font-weight: 700;
  color: #FFFFFF;
  display: inline-block;
  margin-right: 8px;
  letter-spacing: -0.3px;
}

.brand-text .subtext {
  font-size: 13px;
  color: #94A3B8;
  font-weight: 400;
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: 12px;
}

.stats-text {
  font-size: 13px;
  color: #E2E8F0;
  font-weight: 500;
  background: rgba(255, 255, 255, 0.08);
  padding: 6px 14px;
  border-radius: 20px;
  border: 1px solid rgba(255, 255, 255, 0.14);
  letter-spacing: -0.2px;
}

.btn-sync {
  display: flex;
  align-items: center;
  gap: 6px;
  background: rgba(255, 255, 255, 0.12);
  color: #F8FAFC;
  border: 1px solid rgba(255, 255, 255, 0.22);
  padding: 6px 13px;
  border-radius: var(--radius-sm);
  font-size: 12px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.18s ease;
  backdrop-filter: blur(4px);
}

.btn-sync:hover {
  background: rgba(255, 255, 255, 0.22);
  border-color: rgba(255, 255, 255, 0.35);
  color: #FFFFFF;
  transform: translateY(-1px);
}

.btn-sync svg {
  stroke: #F8FAFC;
}

.btn-sync.spinning svg {
  animation: spin 0.8s linear infinite;
}

@keyframes spin {
  100% { transform: rotate(360deg); }
}

@media (max-width: 768px) {
  .navbar {
    flex-direction: column;
    align-items: flex-start;
    gap: 12px;
    padding: 14px 16px;
  }
  .nav-actions {
    width: 100%;
    justify-content: space-between;
  }
}

/* ==================== SEARCH BAR ==================== */
.search-section {
  margin-bottom: 18px;
}

.search-bar {
  display: flex;
  gap: 8px;
}

.search-input-wrap {
  position: relative;
  display: flex;
  align-items: center;
  flex: 1;
  background: #FFFFFF;
  border: 1px solid #CBD5E1;
  border-radius: var(--radius-sm);
  padding: 0 12px;
  transition: border-color 0.15s, box-shadow 0.15s;
}

.search-input-wrap:focus-within {
  border-color: var(--primary);
  box-shadow: 0 0 0 2px rgba(37, 99, 235, 0.15);
}

.search-icon {
  font-size: 16px;
  color: #94A3B8;
  margin-right: 8px;
}

.search-input {
  width: 100%;
  border: none;
  outline: none;
  font-size: 15px;
  padding: 10px 0;
  color: var(--text-primary);
  font-family: inherit;
}

.search-input::placeholder {
  color: #94A3B8;
  font-size: 14px;
}

.btn-clear {
  background: #E2E8F0;
  border: none;
  color: #64748B;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  cursor: pointer;
  font-size: 11px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.btn-clear:hover {
  background: #CBD5E1;
  color: #0F172A;
}

.btn-search {
  background: var(--primary);
  color: #FFFFFF;
  border: none;
  padding: 0 20px;
  border-radius: var(--radius-sm);
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s;
}

.btn-search:hover {
  background: var(--primary-hover);
}

/* Quick Chips */
.quick-chips {
  display: flex;
  align-items: center;
  gap: 6px;
  margin-top: 10px;
  flex-wrap: wrap;
}

.chips-label {
  font-size: 12px;
  color: var(--text-muted);
  margin-right: 2px;
}

.chip {
  background: #FFFFFF;
  border: 1px solid #E2E8F0;
  color: var(--text-secondary);
  padding: 4px 10px;
  border-radius: 14px;
  font-size: 12px;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.15s;
}

.chip:hover, .chip.active-preset {
  background: #EFF6FF;
  border-color: #BFDBFE;
  color: var(--primary);
  font-weight: 600;
}

.chip-sol {
  color: #B91C1C;
}

.chip-sol:hover {
  background: #FEF2F2;
  border-color: #FECACA;
}

.chip-all {
  margin-left: auto;
}

/* ==================== SHEET TOOLBAR ==================== */
.sheet-toolbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 10px 16px;
  background: #FFFFFF;
  border: 1px solid var(--card-border);
  border-radius: var(--radius-sm);
  margin-bottom: 14px;
  flex-wrap: wrap;
  gap: 10px;
}

.toolbar-left {
  display: flex;
  align-items: center;
  gap: 8px;
}

.list-title {
  font-size: 14px;
  font-weight: 700;
  color: var(--text-primary);
}

.result-count {
  font-size: 12px;
  font-weight: 600;
  color: var(--primary);
  background: #EFF6FF;
  padding: 2px 8px;
  border-radius: 10px;
}

.toolbar-filters {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.filter-select {
  background: #FFFFFF;
  border: 1px solid #CBD5E1;
  color: var(--text-secondary);
  padding: 4px 10px;
  border-radius: var(--radius-sm);
  font-size: 12px;
  outline: none;
  font-family: inherit;
  cursor: pointer;
}

.diff-btn-group {
  display: flex;
  border: 1px solid #CBD5E1;
  border-radius: var(--radius-sm);
  overflow: hidden;
  background: #FFFFFF;
}

.diff-btn {
  background: none;
  border: none;
  color: var(--text-muted);
  padding: 4px 9px;
  font-size: 12px;
  font-weight: 500;
  cursor: pointer;
  border-right: 1px solid #E2E8F0;
}

.diff-btn:last-child {
  border-right: none;
}

.diff-btn:hover {
  background: #F1F5F9;
  color: var(--text-primary);
}

.diff-btn.active {
  background: #0F172A;
  color: #FFFFFF;
  font-weight: 600;
}

.toggle-label {
  display: flex;
  align-items: center;
  gap: 5px;
  font-size: 12px;
  color: var(--text-secondary);
  cursor: pointer;
}

.toggle-label input {
  accent-color: var(--btn-sol);
  cursor: pointer;
}

/* ==================== LOADING & EMPTY STATES ==================== */
.loading-state, .empty-state {
  text-align: center;
  padding: 40px 16px;
  background: #FFFFFF;
  border: 1px solid var(--card-border);
  border-radius: var(--radius-md);
  margin-top: 10px;
}

.spinner {
  width: 32px;
  height: 32px;
  border: 3px solid #E2E8F0;
  border-top-color: var(--primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
  margin: 0 auto 12px;
}

.empty-msg {
  font-size: 14px;
  color: var(--text-secondary);
}

.empty-chips {
  display: flex;
  justify-content: center;
  gap: 8px;
  margin-top: 14px;
}

/* ==================== COMPACT PROBLEM CARDS ==================== */
.problems-list {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.problem-card {
  background: #FFFFFF;
  border: 1px solid var(--card-border);
  border-radius: var(--radius-md);
  padding: 14px 18px;
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.03);
  transition: border-color 0.15s;
}

.problem-card:hover {
  border-color: #94A3B8;
}

/* Main Meta & Action Row: 번호, 단원, 난이도, 문제유형, 손풀이영상버튼 */
.card-main-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}

.card-meta-left {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
}

.problem-no-badge {
  font-size: 15px;
  font-weight: 700;
  color: #0F172A;
  background: #F1F5F9;
  border: 1px solid #CBD5E1;
  padding: 3px 9px;
  border-radius: 6px;
}

.badge-unit {
  font-size: 12px;
  font-weight: 600;
  color: #1D4ED8;
  background: #EFF6FF;
  padding: 3px 8px;
  border-radius: 5px;
}

.badge-diff {
  font-size: 12px;
  font-weight: 600;
  padding: 3px 8px;
  border-radius: 5px;
}

.badge-diff.diff-high {
  background: var(--diff-high-bg);
  color: var(--diff-high-text);
}

.badge-diff.diff-mid {
  background: var(--diff-mid-bg);
  color: var(--diff-mid-text);
}

.badge-diff.diff-low {
  background: var(--diff-low-bg);
  color: var(--diff-low-text);
}

.badge-diff.diff-none {
  background: #F1F5F9;
  color: #64748B;
}

.meta-divider {
  color: #CBD5E1;
  font-size: 13px;
}

.meta-type {
  font-size: 13px;
  color: var(--text-primary);
  font-weight: 500;
}

.type-label {
  color: var(--text-muted);
  font-weight: 600;
  margin-right: 4px;
}

/* Action: 손풀이영상 버튼 영역 */
.card-action-right {
  display: flex;
  align-items: center;
  gap: 6px;
  margin-left: auto;
}

/* Simple, clean, eye-friendly solution button */
.btn-sol-cta {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--btn-sol);
  color: #FFFFFF;
  text-decoration: none;
  font-size: 13px;
  font-weight: 700;
  padding: 6px 14px;
  border-radius: 6px;
  border: none;
  cursor: pointer;
  font-family: inherit;
  transition: all 0.15s ease;
}

.btn-sol-cta:hover {
  background: var(--btn-sol-hover);
  transform: translateY(-1px);
}

.sol-missing-badge {
  font-size: 12px;
  color: #94A3B8;
  background: #F1F5F9;
  padding: 4px 10px;
  border-radius: 5px;
}

/* Playing Card Highlight */
.problem-card.card-playing {
  border-color: #3B82F6 !important;
  background: #F8FAFC !important;
  box-shadow: 0 0 0 2px rgba(59, 130, 246, 0.25), 0 4px 12px rgba(59, 130, 246, 0.08) !important;
}

.problem-card.card-playing .problem-no-badge {
  background: #2563EB !important;
  color: #FFFFFF !important;
}

.problem-card.card-playing .btn-sol-cta {
  background: #1D4ED8 !important;
  box-shadow: 0 0 0 2px rgba(37, 99, 235, 0.35);
}

/* Row 2: 출제의도 (난이도, 문제유형과 함께 깔끔하게 표시) */
.card-intent-row {
  margin-top: 10px;
  padding-top: 8px;
  border-top: 1px solid #F1F5F9;
  font-size: 13px;
  color: var(--text-secondary);
  line-height: 1.5;
  display: flex;
  gap: 8px;
}

.intent-label {
  font-weight: 700;
  color: #334155;
  white-space: nowrap;
}

.intent-body {
  color: #475569;
}

/* Embedded Player (콤팩트 토글 영역) */
.card-embed-box {
  margin-top: 12px;
  background: #0F172A;
  border-radius: 6px;
  overflow: hidden;
  max-width: 680px;
}

.player-aspect-ratio {
  position: relative;
  width: 100%;
  padding-top: 56.25%; /* 16:9 */
}

.player-aspect-ratio iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  border: none;
}

/* ==================== FLOATING PIP VIDEO PLAYER (PAD OPTIMIZED) ==================== */
.floating-player {
  position: fixed;
  bottom: 20px;
  right: 20px;
  width: 580px; /* Pad/Desktop standard comfortable size */
  max-width: calc(100vw - 20px);
  background: #0F172A;
  border: 1px solid #334155;
  border-radius: 14px;
  box-shadow: 0 20px 40px -4px rgba(0, 0, 0, 0.6), 0 8px 20px rgba(0, 0, 0, 0.35);
  z-index: 9999;
  overflow: hidden;
  transition: width 0.22s ease, opacity 0.2s ease;
  display: flex;
  flex-direction: column;
}

/* Size Modes */
.floating-player.is-large {
  width: 780px;
}

.floating-player.is-max {
  width: min(96vw, 1040px);
}

.floating-player.is-minimized .fp-body {
  display: none;
}

.floating-player.is-minimized {
  width: 290px;
  border-radius: 10px;
}

.fp-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 14px;
  background: linear-gradient(135deg, #1E293B 0%, #0F172A 100%);
  border-bottom: 1px solid #334155;
  user-select: none;
  -webkit-user-select: none;
  touch-action: none; /* Prevents touch scrolling on tablet when dragging */
  cursor: grab;
}

.fp-header:active {
  cursor: grabbing;
}

.fp-title-group {
  display: flex;
  align-items: center;
  gap: 8px;
  overflow: hidden;
  white-space: nowrap;
  text-overflow: ellipsis;
  flex: 1;
  pointer-events: none; /* Allows dragging by clicking anywhere on title */
}

.fp-drag-handle {
  color: #94A3B8;
  font-size: 15px;
  letter-spacing: -2px;
  opacity: 0.85;
  flex-shrink: 0;
  user-select: none;
}

.fp-badge {
  background: #2563EB;
  color: #FFFFFF;
  font-size: 11px;
  font-weight: 700;
  padding: 3px 8px;
  border-radius: 4px;
  flex-shrink: 0;
  letter-spacing: -0.2px;
}

.fp-title {
  font-size: 12.5px;
  font-weight: 600;
  color: #F8FAFC;
  overflow: hidden;
  text-overflow: ellipsis;
  letter-spacing: -0.2px;
}

.fp-actions {
  display: flex;
  align-items: center;
  gap: 6px;
  margin-left: 8px;
  flex-shrink: 0;
}

/* Touch-friendly buttons for iPad/tablet fingers and stylus */
.fp-action-btn {
  background: rgba(255, 255, 255, 0.1);
  color: #CBD5E1;
  border: 1px solid rgba(255, 255, 255, 0.16);
  width: 32px;
  height: 32px;
  border-radius: 7px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 13px;
  font-weight: 700;
  cursor: pointer;
  text-decoration: none;
  transition: all 0.15s ease;
  line-height: 1;
}

.fp-action-btn:hover {
  background: rgba(255, 255, 255, 0.22);
  color: #FFFFFF;
  border-color: rgba(255, 255, 255, 0.35);
  transform: translateY(-1px);
}

.fp-action-btn.fp-close:hover {
  background: #DC2626;
  border-color: #EF4444;
  color: #FFFFFF;
}

.fp-body {
  position: relative;
  width: 100%;
  background: #000000;
}

.fp-iframe-wrap {
  position: relative;
  width: 100%;
  padding-top: 56.25%; /* 16:9 ratio */
}

.fp-iframe-wrap iframe,
.fp-iframe-wrap #fpPlayerContainer,
.fp-iframe-wrap #fpPlayerContainer iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  border: none;
}

@media (max-width: 768px) {
  .floating-player {
    width: calc(100vw - 20px);
    max-width: 100%;
  }
  .floating-player.is-large,
  .floating-player.is-max {
    width: calc(100vw - 20px);
  }
}

/* Toast */
.toast {
  position: fixed;
  bottom: 25px;
  left: 50%;
  transform: translateX(-50%);
  background: #0F172A;
  color: #FFFFFF;
  padding: 8px 18px;
  border-radius: 20px;
  font-size: 13px;
  font-weight: 500;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
  z-index: 2000;
}

.hidden {
  display: none !important;
}

/* ==================== PRINT STYLES ==================== */
@media print {
  body {
    background: #FFFFFF !important;
    color: #000000 !important;
    padding: 0;
  }
  .no-print, .floating-player {
    display: none !important;
  }
  .app-container {
    max-width: 100% !important;
    padding: 0 !important;
  }
  .problem-card {
    border: 1px solid #D1D5DB !important;
    box-shadow: none !important;
    page-break-inside: avoid;
    margin-bottom: 12px;
    padding: 10px 14px;
  }
  .btn-sol-cta {
    display: none !important;
  }
  .card-embed-box {
    display: none !important;
  }
  .problem-no-badge {
    background: #EEEEEE !important;
    color: #000000 !important;
  }
}