/* ============================================================
   知行学伴 OutLearn — 设计系统
   设计哲学：温暖科技，静默陪伴
   主色: #4F46E5 (Indigo) | AI标记: #F59E0B (Amber) | 强调: #0D9488 (Teal)
   ============================================================ */

/* --- CSS Variables --- */
:root {
  --primary: #4F46E5;
  --primary-hover: #4338CA;
  --primary-light: #EEF2FF;
  --amber: #F59E0B;
  --amber-light: #FEF3C7;
  --amber-dark: #D97706;
  --teal: #0D9488;
  --teal-light: #CCFBF1;
  --purple: #7C3AED;
  --purple-light: #F3E8FF;

  --gray-50: #FAFAF9;
  --gray-100: #F5F5F4;
  --gray-200: #E7E5E4;
  --gray-300: #D6D3D1;
  --gray-400: #A8A29E;
  --gray-500: #78716C;
  --gray-600: #57534E;
  --gray-700: #44403C;
  --gray-800: #292524;
  --gray-900: #1C1917;

  --red: #DC2626;
  --red-light: #FEE2E2;

  --font-sans: 'Inter', 'Noto Sans SC', 'Microsoft YaHei', 'PingFang SC', sans-serif;
  --font-mono: 'JetBrains Mono', 'Consolas', monospace;

  --radius-sm: 6px;
  --radius: 8px;
  --radius-lg: 12px;
  --radius-xl: 16px;

  --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
  --shadow: 0 1px 3px rgba(0,0,0,0.1), 0 1px 2px rgba(0,0,0,0.06);
  --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.1), 0 2px 4px -2px rgba(0,0,0,0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.1), 0 4px 6px -4px rgba(0,0,0,0.1);

  --transition: 0.2s ease;
}

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

html { font-size: 16px; -webkit-font-smoothing: antialiased; }

body {
  font-family: var(--font-sans);
  color: var(--gray-800);
  background: var(--gray-50);
  line-height: 1.6;
  overflow: hidden;
  height: 100vh;
}

/* --- Topbar --- */
.topbar {
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 20px;
  background: white;
  border-bottom: 1px solid var(--gray-200);
  z-index: 100;
  position: relative;
}

.topbar-left {
  display: flex;
  align-items: center;
  gap: 16px;
}

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

.brand-icon { flex-shrink: 0; }

.brand-name {
  font-size: 18px;
  font-weight: 700;
  color: var(--gray-900);
  letter-spacing: -0.3px;
}

.brand-sub {
  font-size: 12px;
  color: var(--gray-400);
  font-weight: 500;
  margin-left: -4px;
}

.scene-badge {
  font-size: 12px;
  font-weight: 600;
  padding: 3px 10px;
  border-radius: 20px;
  background: var(--primary-light);
  color: var(--primary);
  transition: all var(--transition);
}

.scene-badge.exam-scene { background: var(--teal-light); color: var(--teal); }
.scene-badge.classroom-scene { background: var(--purple-light); color: var(--purple); }

.topbar-nav {
  display: flex;
  gap: 4px;
}

.nav-btn {
  font-family: var(--font-sans);
  font-size: 14px;
  font-weight: 500;
  padding: 6px 14px;
  border: none;
  border-radius: var(--radius);
  background: transparent;
  color: var(--gray-500);
  cursor: pointer;
  transition: all var(--transition);
}

.nav-btn:hover { background: var(--gray-100); color: var(--gray-700); }
.nav-btn.active { background: var(--primary); color: white; }

.topbar-right {
  display: flex;
  align-items: center;
}

.ai-badge {
  font-size: 11px;
  font-weight: 600;
  padding: 3px 8px;
  border-radius: var(--radius-sm);
  background: var(--amber-light);
  color: var(--amber-dark);
}

/* --- App Layout --- */
.app-layout {
  display: flex;
  height: calc(100vh - 56px);
  overflow: hidden;
}

/* --- Sidebar --- */
.sidebar {
  width: 240px;
  background: white;
  border-right: 1px solid var(--gray-200);
  padding: 16px;
  overflow-y: auto;
  flex-shrink: 0;
}

.sidebar-section {
  margin-bottom: 24px;
}

.sidebar-title {
  font-size: 11px;
  font-weight: 600;
  color: var(--gray-400);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 10px;
}

.scene-selector {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.scene-btn {
  font-family: var(--font-sans);
  font-size: 13px;
  font-weight: 500;
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 12px;
  border: 1px solid transparent;
  border-radius: var(--radius);
  background: transparent;
  color: var(--gray-600);
  cursor: pointer;
  transition: all var(--transition);
  text-align: left;
  width: 100%;
}

.scene-btn:hover { background: var(--gray-100); }
.scene-btn.active { background: var(--primary-light); color: var(--primary); border-color: var(--primary); }

.history-list { font-size: 13px; }

.history-item {
  padding: 8px 10px;
  font-size: 13px;
  color: var(--gray-600);
  cursor: pointer;
  border-radius: 6px;
  margin-bottom: 2px;
  transition: all var(--transition);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.history-item:hover { background: var(--gray-100); }

.history-time {
  font-size: 11px;
  color: var(--gray-400);
  flex-shrink: 0;
  margin-left: 8px;
}

.empty-text {
  font-size: 13px;
  color: var(--gray-400);
  text-align: center;
  padding: 24px 0;
}

/* --- Main Content --- */
.main-content {
  flex: 1;
  overflow-y: auto;
  padding: 24px;
  background: var(--gray-50);
}

.panel {
  display: none;
}

.panel.active {
  display: block;
  animation: fadeIn 0.3s ease;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

.panel-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 8px;
}

.panel-header h2 {
  font-size: 22px;
  font-weight: 700;
  color: var(--gray-900);
  letter-spacing: -0.3px;
}

.panel-actions {
  display: flex;
  align-items: center;
  gap: 8px;
}

.panel-summary {
  font-size: 14px;
  color: var(--gray-500);
  margin-bottom: 20px;
}

/* --- AI Label --- */
.ai-label {
  font-size: 11px;
  font-weight: 600;
  padding: 3px 10px;
  border-radius: 20px;
  background: var(--amber-light);
  color: var(--amber-dark);
  border: 1px solid var(--amber);
  display: flex;
  align-items: center;
  gap: 4px;
}

.ai-label::before {
  content: '';
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--amber);
}

/* --- Buttons --- */
.btn {
  font-family: var(--font-sans);
  font-size: 14px;
  font-weight: 500;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 8px 16px;
  border: none;
  border-radius: var(--radius);
  cursor: pointer;
  transition: all var(--transition);
  white-space: nowrap;
}

.btn-primary {
  background: var(--primary);
  color: white;
}

.btn-primary:hover { background: var(--primary-hover); }
.btn-primary:disabled { opacity: 0.5; cursor: not-allowed; }

.btn-ghost {
  background: transparent;
  color: var(--gray-600);
  border: 1px solid var(--gray-200);
}

.btn-ghost:hover { background: var(--gray-100); }

.btn-sm { font-size: 12px; padding: 5px 10px; }

.btn-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border: none;
  border-radius: var(--radius);
  background: transparent;
  color: var(--gray-400);
  cursor: pointer;
  transition: all var(--transition);
}

.btn-icon:hover { background: var(--gray-100); color: var(--gray-600); }

/* --- Input Area --- */
.input-tabs {
  display: flex;
  gap: 0;
  margin-bottom: 0;
  background: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius) var(--radius) 0 0;
  overflow: hidden;
}

.input-tab {
  font-family: var(--font-sans);
  font-size: 14px;
  font-weight: 500;
  padding: 10px 20px;
  border: none;
  background: transparent;
  color: var(--gray-500);
  cursor: pointer;
  transition: all var(--transition);
  border-bottom: 2px solid transparent;
}

.input-tab:hover { color: var(--gray-700); }
.input-tab.active { color: var(--primary); border-bottom-color: var(--primary); background: var(--primary-light); }

.input-area {
  display: none;
  background: white;
  border: 1px solid var(--gray-200);
  border-top: none;
  border-radius: 0 0 var(--radius-lg) var(--radius-lg);
  padding: 20px;
}

.input-area.active { display: block; }

#textInput {
  font-family: var(--font-sans);
  width: 100%;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius);
  padding: 14px;
  font-size: 14px;
  line-height: 1.7;
  resize: vertical;
  color: var(--gray-800);
  transition: border-color var(--transition);
}

#textInput:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-light);
}

.input-actions {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 12px;
}

.char-count { font-size: 12px; color: var(--gray-400); }

/* Bili input */
.bili-input-group {
  display: flex;
  gap: 10px;
  margin-bottom: 16px;
}

.bili-input-group input {
  flex: 1;
  font-family: var(--font-sans);
  font-size: 14px;
  padding: 10px 14px;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius);
  color: var(--gray-800);
  transition: border-color var(--transition);
}

.bili-input-group input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-light);
}

.bili-page-select {
  font-family: var(--font-sans);
  font-size: 14px;
  padding: 8px 12px;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius);
  background: white;
  color: var(--gray-800);
  min-width: 80px;
}

.bili-video-info {
  padding: 12px 16px;
  background: var(--gray-50);
  border-radius: var(--radius);
  margin-bottom: 12px;
  font-size: 13px;
  color: var(--gray-600);
}

.bili-video-info .bili-video-title {
  font-weight: 600;
  color: var(--gray-800);
  margin-bottom: 4px;
}

.bili-video-info .bili-video-meta {
  font-size: 12px;
  color: var(--gray-400);
}

.bili-player {
  border-radius: var(--radius-lg);
  overflow: hidden;
  background: var(--gray-900);
  min-height: 360px;
}

.bili-player iframe {
  width: 100%;
  height: 450px;
  border: none;
}

/* --- Transcript Area (讲师原话) --- */
.transcript-area {
  margin-top: 16px;
  background: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-lg);
  overflow: hidden;
}

.transcript-header {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 16px;
  background: var(--primary-light);
  cursor: pointer;
  user-select: none;
  transition: background var(--transition);
}

.transcript-header:hover {
  background: #E0E7FF;
}

.transcript-title {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 14px;
  font-weight: 600;
  color: var(--primary);
  flex: 1;
}

.transcript-meta {
  font-size: 12px;
  color: var(--gray-400);
  margin-right: 8px;
}

.transcript-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 24px;
  height: 24px;
  border: none;
  border-radius: var(--radius-sm);
  background: transparent;
  color: var(--gray-400);
  cursor: pointer;
  transition: all var(--transition);
}

.transcript-toggle:hover {
  background: rgba(0,0,0,0.05);
  color: var(--gray-600);
}

/* 转录操作按钮（复制、编辑） */
.transcript-actions {
  display: flex;
  align-items: center;
  gap: 4px;
}

.transcript-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  border: none;
  border-radius: var(--radius-sm);
  background: transparent;
  color: var(--gray-400);
  cursor: pointer;
  transition: all var(--transition);
}

.transcript-btn:hover {
  background: rgba(99,102,241,0.1);
  color: var(--primary);
}

/* 编辑模式 textarea */
.transcript-editor {
  width: 100%;
  min-height: 200px;
  max-height: 500px;
  padding: 12px 16px;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-md);
  font-size: 14px;
  line-height: 1.9;
  color: var(--gray-700);
  font-family: inherit;
  resize: vertical;
  outline: none;
  box-sizing: border-box;
}

.transcript-editor:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(99,102,241,0.1);
}

/* =============================================
   时间戳同步样式（讲师原话 + 视频播放联动）
   ============================================= */
.ts-transcript {
  padding: 4px 0;
}

.ts-seg {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 6px 12px;
  border-radius: 6px;
  cursor: default;
  transition: background 0.15s;
  border-left: 3px solid transparent;
  margin: 2px 0;
}

.ts-seg:hover {
  background: rgba(99,102,241,0.04);
}

.ts-seg.active {
  background: rgba(99,102,241,0.08);
  border-left-color: var(--primary);
}

.ts-seg.active .ts-text {
  color: var(--primary);
}

.ts-badge {
  flex-shrink: 0;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 44px;
  padding: 2px 8px;
  background: var(--primary-light, #EEF2FF);
  color: var(--primary, #6366F1);
  border-radius: 4px;
  font-size: 12px;
  font-weight: 600;
  font-family: 'SF Mono', 'Consolas', 'Monaco', monospace;
  cursor: pointer;
  transition: all 0.15s;
  user-select: none;
}

.ts-badge:hover {
  background: var(--primary, #6366F1);
  color: #fff;
  transform: scale(1.05);
  box-shadow: 0 2px 6px rgba(99,102,241,0.25);
}

.ts-text {
  flex: 1;
  font-size: 14px;
  line-height: 1.9;
  color: var(--gray-600, #4B5563);
  word-break: break-word;
}

.ts-long .ts-text {
  line-height: 1.7;
  font-size: 13.5px;
}

.hidden { display: none !important; }

.transcript-body {
  padding: 16px 20px;
  max-height: 320px;
  overflow-y: auto;
  font-size: 14px;
  line-height: 1.9;
  color: var(--gray-700);
  white-space: pre-wrap;
  word-break: break-word;
  border-top: 1px solid var(--gray-100);
}

.transcript-area.collapsed .transcript-body {
  display: none;
}

.transcript-area.collapsed .transcript-toggle svg {
  transform: rotate(-90deg);
}

.transcript-loading .spinner {
  box-shadow: 0 1px 3px rgba(0,0,0,0.08);
}

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

/* --- Loading Overlay --- */
.loading-overlay {
  display: none;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 48px 24px;
  gap: 16px;
}

.loading-overlay.active {
  display: flex;
}

.loading-spinner {
  width: 40px;
  height: 40px;
  border: 3px solid var(--gray-200);
  border-top-color: var(--primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

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

/* 下载进度脉冲动画 */
@keyframes pulse-progress {
  0%, 100% { transform: translateX(0); }
  50% { transform: translateX(120%); }
}

#loadingText {
  font-size: 14px;
  color: var(--gray-500);
  animation: pulse 1.5s ease infinite;
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

/* --- Knowledge Framework Tree --- */
.framework-tree {
  background: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-lg);
  padding: 20px;
}

.fw-meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 12px;
}

.fw-struct-label {
  font-size: 12px;
  color: var(--gray-400);
  display: flex;
  align-items: center;
  gap: 4px;
}

.fw-node-count {
  font-size: 12px;
  color: var(--primary);
  background: var(--primary-light);
  padding: 2px 10px;
  border-radius: 20px;
  font-weight: 600;
}

.fw-update-info {
  font-size: 12px;
  color: var(--gray-400);
  margin-left: auto;
}

.fw-keywords {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  margin-bottom: 16px;
}

.fw-keyword-tag {
  font-size: 12px;
  padding: 3px 12px;
  background: var(--primary-light);
  color: var(--primary);
  border-radius: 20px;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition);
}

.fw-keyword-tag:hover {
  background: var(--primary);
  color: white;
}

.fw-stats-bar {
  display: flex;
  gap: 16px;
  padding: 10px 14px;
  background: var(--gray-50);
  border-radius: var(--radius);
  margin-bottom: 16px;
  font-size: 13px;
  color: var(--gray-500);
}

.fw-stats-bar span {
  display: flex;
  align-items: center;
  gap: 4px;
}

.fw-node {
  margin-bottom: 1px;
}

.fw-node-header {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 12px;
  border-radius: var(--radius);
  cursor: pointer;
  transition: all var(--transition);
  font-size: 14px;
  font-weight: 500;
  color: var(--gray-700);
  position: relative;
}

.fw-node-header:hover { background: var(--gray-100); }

.fw-node-header.key-node {
  color: var(--amber-dark);
  font-weight: 600;
}

.fw-node-header .key-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--amber);
  flex-shrink: 0;
}

.fw-toggle-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 18px;
  height: 18px;
  flex-shrink: 0;
  transition: transform 0.2s ease;
}

.fw-toggle-btn svg {
  transition: transform 0.2s ease;
}

.fw-toggle-placeholder {
  width: 18px;
  flex-shrink: 0;
}

.fw-node-title-text {
  flex: 1;
}

.fw-node-actions {
  display: flex;
  gap: 4px;
  opacity: 0;
  transition: opacity var(--transition);
}

.fw-node-header:hover .fw-node-actions {
  opacity: 1;
}

.fw-action-btn {
  font-size: 12px;
  padding: 2px 6px;
  border: 1px solid var(--gray-200);
  border-radius: 4px;
  background: white;
  cursor: pointer;
  transition: all var(--transition);
}

.fw-action-btn:hover {
  background: var(--amber-light);
  border-color: var(--amber);
}

.fw-node.level-0 .fw-node-header {
  font-size: 16px;
  font-weight: 700;
  color: var(--primary);
  background: var(--primary-light);
  border-radius: var(--radius);
}

.fw-node.level-1 .fw-node-header {
  font-size: 14px;
  font-weight: 600;
  color: var(--gray-800);
}

.fw-node.level-2 .fw-node-header {
  font-size: 13px;
  font-weight: 500;
  color: var(--gray-600);
}

.fw-node.level-3 .fw-node-header {
  font-size: 12px;
  color: var(--gray-500);
}

.fw-children {
  margin-left: 0;
  overflow: hidden;
  transition: max-height 0.3s ease, opacity 0.3s ease;
}

.fw-children.collapsed {
  max-height: 0 !important;
  opacity: 0;
  pointer-events: none;
}

/* --- Reference (Quick Reference Manual) --- */
.reference-content {
  display: flex;
  flex-direction: column;
  gap: 20px;
}

.ref-card {
  background: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-lg);
  padding: 20px;
}

.ref-card-header {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 14px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--gray-100);
}

.ref-card-header h3 {
  font-size: 16px;
  font-weight: 600;
  color: var(--gray-800);
  flex: 1;
}

.ref-card-badge {
  font-size: 12px;
  color: var(--gray-400);
  background: var(--gray-100);
  padding: 2px 8px;
  border-radius: 10px;
}

.ref-card-header .ref-icon {
  width: 28px;
  height: 28px;
  border-radius: var(--radius);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 14px;
}

.quick-table {
  width: 100%;
  border-collapse: collapse;
}

.quick-table th, .quick-table td {
  padding: 8px 12px;
  text-align: left;
  font-size: 13px;
  border-bottom: 1px solid var(--gray-100);
}

.quick-table th {
  font-weight: 600;
  color: var(--gray-500);
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.3px;
}

.quick-table td:first-child {
  font-weight: 600;
  color: var(--primary);
  width: 180px;
}

.quick-table td:last-child {
  color: var(--gray-600);
}

.ref-steps { list-style: none; }
.ref-steps li {
  display: flex;
  gap: 10px;
  padding: 8px 0;
  font-size: 14px;
  color: var(--gray-700);
  border-bottom: 1px solid var(--gray-100);
}

.ref-steps .step-num {
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: var(--primary);
  color: white;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 12px;
  font-weight: 600;
  flex-shrink: 0;
}

.ref-pitfalls {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.ref-pitfalls li {
  display: flex;
  align-items: flex-start;
  gap: 8px;
  font-size: 13px;
  color: var(--gray-700);
  padding: 10px;
  background: var(--red-light);
  border-radius: var(--radius);
  border-left: 3px solid var(--red);
}

.ref-pitfalls li::before { content: '⚠️'; flex-shrink: 0; }

.ref-mnemonic {
  font-size: 14px;
  color: var(--teal);
  background: var(--teal-light);
  padding: 14px;
  border-radius: var(--radius);
  border-left: 3px solid var(--teal);
}

/* --- Feynman --- */
.feynman-select {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 20px;
  padding: 16px;
  background: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-lg);
}

.feynman-select label {
  font-size: 14px;
  font-weight: 500;
  color: var(--gray-600);
  white-space: nowrap;
}

.feynman-select select {
  flex: 1;
  font-family: var(--font-sans);
  font-size: 14px;
  padding: 8px 12px;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius);
  color: var(--gray-800);
  background: white;
}

.feynman-content {
  background: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-lg);
  padding: 24px;
}

.feynman-node-label {
  font-size: 14px;
  color: var(--primary);
  background: var(--primary-light);
  padding: 8px 14px;
  border-radius: var(--radius);
  margin-bottom: 20px;
  display: inline-block;
}

.feynman-block {
  margin-bottom: 20px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--gray-100);
}

.feynman-block:last-child {
  margin-bottom: 0;
  padding-bottom: 0;
  border-bottom: none;
}

.feynman-block h3 {
  font-size: 12px;
  font-weight: 600;
  color: var(--gray-400);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 8px;
}

.feynman-block p {
  font-size: 14px;
  color: var(--gray-700);
  line-height: 1.8;
}

.analogy-block {
  background: var(--amber-light);
  border-left: 3px solid var(--amber);
  padding: 14px;
  border-radius: 0 var(--radius) var(--radius) 0;
  margin: 10px 0;
}

.one-sentence-box {
  background: var(--primary-light);
  padding: 14px 18px;
  border-radius: var(--radius);
  font-size: 16px;
  font-weight: 600;
  color: var(--primary);
  text-align: center;
  margin: 16px 0;
}

.check-questions {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.check-questions li {
  font-size: 14px;
  padding: 10px 14px;
  background: var(--gray-100);
  border-radius: var(--radius);
  color: var(--gray-600);
}

.check-questions li::before {
  content: '💡 ';
  font-size: 12px;
}

/* --- Exercises --- */
.exercise-stats-bar {
  display: flex;
  gap: 16px;
  padding: 12px 16px;
  background: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-lg);
  margin-bottom: 16px;
  font-size: 13px;
  flex-wrap: wrap;
}

.exercise-stats-bar .stat-item {
  display: flex;
  align-items: center;
  gap: 4px;
  color: var(--gray-500);
}

.stat-item.correct-stat { color: var(--teal); }
.stat-item.incorrect-stat { color: var(--red); }

.exercise-controls {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 20px;
  padding: 16px;
  background: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-lg);
  flex-wrap: wrap;
}
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 20px;
  padding: 16px;
  background: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-lg);
}

.exercise-controls select {
  font-family: var(--font-sans);
  font-size: 14px;
  padding: 8px 12px;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius);
  color: var(--gray-800);
  background: white;
}

.exercise-list {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.exercise-card {
  background: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-lg);
  padding: 20px;
  transition: all var(--transition);
}

.exercise-card.answered {
  border-color: var(--primary);
  box-shadow: 0 0 0 2px var(--primary-light);
}

.exercise-card.correct { border-color: var(--teal); }
.exercise-card.incorrect { border-color: var(--red); }

.exercise-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 12px;
}

.exercise-type {
  font-size: 11px;
  font-weight: 600;
  padding: 2px 8px;
  border-radius: 20px;
}

.type-choice { background: var(--primary-light); color: var(--primary); }
.type-judge { background: var(--amber-light); color: var(--amber-dark); }
.type-short_answer { background: var(--teal-light); color: var(--teal); }

.exercise-question {
  font-size: 15px;
  font-weight: 600;
  color: var(--gray-800);
  margin-bottom: 14px;
  line-height: 1.6;
}

.exercise-options {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin-bottom: 14px;
}

.exercise-option {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 14px;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius);
  cursor: pointer;
  font-size: 14px;
  color: var(--gray-700);
  transition: all var(--transition);
}

.exercise-option:hover { background: var(--gray-50); border-color: var(--gray-300); }
.exercise-option.selected { background: var(--primary-light); border-color: var(--primary); color: var(--primary); }
.exercise-option.correct-answer { background: var(--teal-light); border-color: var(--teal); color: var(--teal); }
.exercise-option.wrong-answer { background: var(--red-light); border-color: var(--red); color: var(--red); }

.exercise-input-answer {
  width: 100%;
  font-family: var(--font-sans);
  font-size: 14px;
  padding: 10px 14px;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius);
  margin-bottom: 12px;
  color: var(--gray-800);
}

.exercise-input-answer:focus {
  outline: none;
  border-color: var(--primary);
}

.exercise-hint {
  font-size: 13px;
  color: var(--gray-500);
  padding: 10px;
  background: var(--amber-light);
  border-radius: var(--radius);
  margin-bottom: 12px;
}

.exercise-explanation {
  font-size: 13px;
  color: var(--gray-600);
  padding: 12px;
  background: var(--gray-100);
  border-radius: var(--radius);
  border-left: 3px solid var(--primary);
  line-height: 1.7;
  display: none;
}

.exercise-explanation.visible { display: block; }

.explanation-correct {
  color: var(--teal);
  margin-bottom: 6px;
}

.explanation-detail {
  color: var(--gray-600);
  line-height: 1.7;
}

.explanation-kp {
  font-size: 12px;
  color: var(--gray-400);
  margin-top: 8px;
  padding-top: 6px;
  border-top: 1px solid var(--gray-200);
}

.exercise-actions {
  display: flex;
  gap: 8px;
  margin-top: 12px;
}

/* --- Detail Panel --- */
.detail-panel {
  width: 320px;
  background: white;
  border-left: 1px solid var(--gray-200);
  padding: 16px;
  display: flex;
  flex-direction: column;
  flex-shrink: 0;
  transition: all var(--transition);
}

.detail-panel.collapsed {
  width: 0;
  padding: 0;
  overflow: hidden;
}

.detail-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 12px;
}

.detail-header h3 {
  font-size: 15px;
  font-weight: 600;
  color: var(--gray-800);
}

.query-input {
  display: flex;
  gap: 8px;
  margin-bottom: 16px;
}

.query-input input {
  flex: 1;
  font-family: var(--font-sans);
  font-size: 13px;
  padding: 8px 12px;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius);
  color: var(--gray-800);
}

.query-input input:focus {
  outline: none;
  border-color: var(--primary);
}

.query-result {
  flex: 1;
  overflow-y: auto;
  background: var(--gray-50);
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-lg);
  padding: 14px;
}

.query-result .answer-text { font-size: 14px; color: var(--gray-700); line-height: 1.7; }
.query-result .source-info { font-size: 12px; color: var(--gray-400); margin-top: 10px; padding-top: 8px; border-top: 1px solid var(--gray-200); }
.query-result .extended-info { font-size: 13px; color: var(--teal); margin-top: 8px; padding: 10px; background: var(--teal-light); border-radius: var(--radius); }

.query-result .query-error { font-size: 13px; color: var(--red); }

/* --- Feedback --- */
.feedback-section {
  margin-top: 16px;
  padding-top: 12px;
  border-top: 1px solid var(--gray-200);
}

.feedback-title {
  font-size: 12px;
  color: var(--gray-400);
  margin-bottom: 8px;
}

.feedback-btns {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
}

.feedback-btn {
  font-family: var(--font-sans);
  font-size: 12px;
  padding: 4px 10px;
  border: 1px solid var(--gray-200);
  border-radius: 14px;
  background: white;
  color: var(--gray-500);
  cursor: pointer;
  transition: all var(--transition);
}

.feedback-btn:hover {
  background: var(--gray-100);
  border-color: var(--gray-300);
}

.feedback-btn.active {
  background: var(--primary-light);
  border-color: var(--primary);
  color: var(--primary);
}

/* --- Exercise Result Summary --- */
.exercise-result-summary {
  margin-top: 20px;
  padding: 20px;
  background: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius-lg);
  text-align: center;
}

.exercise-result-summary .result-score {
  font-size: 48px;
  font-weight: 700;
  color: var(--primary);
  line-height: 1;
}

.exercise-result-summary .result-label {
  font-size: 14px;
  color: var(--gray-500);
  margin: 8px 0 16px;
}

.exercise-result-summary .result-breakdown {
  display: flex;
  justify-content: center;
  gap: 24px;
  font-size: 13px;
  color: var(--gray-600);
}

/* --- Responsive --- */
@media (max-width: 1200px) {
  .detail-panel { width: 280px; }
}

@media (max-width: 1024px) {
  .sidebar { width: 200px; padding: 12px; }
  .detail-panel { width: 260px; padding: 12px; }
  .main-content { padding: 16px; }
}

@media (max-width: 860px) {
  .sidebar { display: none; }
  .detail-panel {
    position: fixed;
    right: 0;
    top: 56px;
    bottom: 0;
    width: 300px;
    z-index: 50;
    box-shadow: -4px 0 12px rgba(0,0,0,0.1);
    transform: translateX(0);
  }
  .detail-panel.collapsed {
    transform: translateX(100%);
    width: 300px;
    padding: 12px;
    overflow: hidden;
  }
}

@media (max-width: 640px) {
  .topbar {
    padding: 0 12px;
  }
  .topbar-nav {
    display: none;
  }
  .brand-sub { display: none; }
  .main-content { padding: 12px; }

  /* 移动端底部导航 */
  .mobile-nav {
    display: flex;
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    height: 56px;
    background: white;
    border-top: 1px solid var(--gray-200);
    z-index: 100;
    justify-content: space-around;
    align-items: center;
  }

  .mobile-nav-btn {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 2px;
    font-size: 10px;
    color: var(--gray-400);
    border: none;
    background: none;
    cursor: pointer;
    padding: 4px 8px;
  }

  .mobile-nav-btn.active {
    color: var(--primary);
  }

  .mobile-nav-btn svg {
    width: 20px;
    height: 20px;
  }

  .app-layout {
    height: calc(100vh - 56px - 56px);
  }

  .detail-panel {
    top: 56px;
    bottom: 56px;
    width: 100%;
  }

  .detail-panel.collapsed {
    transform: translateX(100%);
    width: 100%;
  }

  .panel-header h2 { font-size: 18px; }

  .input-tabs { overflow-x: auto; }
  .input-tab { white-space: nowrap; padding: 10px 14px; font-size: 13px; }

  .bili-input-group {
    flex-direction: column;
  }

  .exercise-controls {
    flex-direction: column;
    align-items: stretch;
  }

  .feynman-select {
    flex-direction: column;
    align-items: stretch;
  }
}

/* 显示移动端导航的条件（通过JS控制） */
.mobile-nav { display: none; }
@media (max-width: 640px) {
  .mobile-nav { display: flex; }
}

/* --- Print styles for export --- */
@media print {
  .topbar, .sidebar, .detail-panel, .mobile-nav, .exercise-actions,
  .btn, .input-tabs, .input-area, .loading-overlay { display: none !important; }
  .app-layout { display: block; height: auto; }
  .main-content { overflow: visible; padding: 0; }
  .panel { display: block !important; }
}

/* --- Scrollbar --- */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--gray-300); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--gray-400); }