/**
 * 考试在线练习系统 - 高级视觉设计系统 (Vanilla CSS)
 * 包含全局变量、深浅色模式适配、毛玻璃质感、丝滑微动画与响应式排版
 */

/* ==========================================================================
   1. 全局设计令牌 (Design Tokens)
   ========================================================================== */
:root {
  /* 调色盘 - 基于 HSL 精密微调 */
  --hue-primary: 217;
  --hue-success: 142;
  --hue-danger: 0;
  --hue-warning: 38;

  /* 亮色模式 (Light Theme) */
  --bg-base: hsl(210, 20%, 98%);
  --bg-surface: hsl(0, 0%, 100%);
  --bg-surface-hover: hsl(210, 16%, 95%);
  --bg-surface-active: hsl(210, 16%, 90%);
  
  --text-main: hsl(217, 33%, 17%);
  --text-muted: hsl(215, 16%, 47%);
  --text-inverse: hsl(0, 0%, 100%);

  --border-color: hsl(214, 20%, 90%);
  --border-color-hover: hsl(214, 20%, 80%);

  /* 品牌主色 */
  --primary: hsl(var(--hue-primary), 91%, 60%);
  --primary-hover: hsl(var(--hue-primary), 91%, 53%);
  --primary-light: hsl(var(--hue-primary), 91%, 95%);
  --primary-alpha: hsla(var(--hue-primary), 91%, 60%, 0.15);

  /* 功能反馈色 */
  --success: hsl(var(--hue-success), 71%, 45%);
  --success-light: hsl(var(--hue-success), 71%, 94%);
  --danger: hsl(var(--hue-danger), 84%, 60%);
  --danger-light: hsl(var(--hue-danger), 84%, 95%);
  --warning: hsl(var(--hue-warning), 92%, 50%);

  /* 阴影层级系统 */
  --shadow-sm: 0 1px 2px 0 hsla(217, 33%, 17%, 0.05);
  --shadow-md: 0 4px 6px -1px hsla(217, 33%, 17%, 0.08), 0 2px 4px -2px hsla(217, 33%, 17%, 0.04);
  --shadow-lg: 0 10px 15px -3px hsla(217, 33%, 17%, 0.1), 0 4px 6px -4px hsla(217, 33%, 17%, 0.05);
  --shadow-glass: 0 8px 32px 0 hsla(217, 33%, 17%, 0.08);

  /* 基础动画时间 */
  --transition-fast: 0.15s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-normal: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 0.4s cubic-bezier(0.4, 0, 0.2, 1);

  /* 布局令牌 */
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-full: 9999px;
  --header-height: 64px;
}

/* 深色模式 (Dark Theme) */
[data-theme="dark"] {
  --bg-base: hsl(217, 33%, 9%);
  --bg-surface: hsl(217, 24%, 14%);
  --bg-surface-hover: hsl(217, 24%, 20%);
  --bg-surface-active: hsl(217, 24%, 26%);

  --text-main: hsl(210, 20%, 98%);
  --text-muted: hsl(215, 16%, 65%);

  --border-color: hsl(217, 24%, 22%);
  --border-color-hover: hsl(217, 24%, 30%);

  --primary: hsl(var(--hue-primary), 85%, 62%);
  --primary-light: hsla(var(--hue-primary), 85%, 62%, 0.15);
  
  --success-light: hsla(var(--hue-success), 71%, 45%, 0.15);
  --danger-light: hsla(var(--hue-danger), 84%, 60%, 0.15);

  --shadow-sm: 0 1px 2px 0 hsla(0, 0%, 0%, 0.5);
  --shadow-md: 0 4px 6px -1px hsla(0, 0%, 0%, 0.4), 0 2px 4px -2px hsla(0, 0%, 0%, 0.2);
  --shadow-lg: 0 10px 15px -3px hsla(0, 0%, 0%, 0.5), 0 4px 6px -4px hsla(0, 0%, 0%, 0.3);
  --shadow-glass: 0 8px 32px 0 hsla(0, 0%, 0%, 0.4);
}

/* ==========================================================================
   2. 基础元素样式重置 (Reset & Base)
   ========================================================================== */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background-color: var(--bg-base);
  color: var(--text-main);
  line-height: 1.6;
  transition: background-color var(--transition-normal), color var(--transition-normal);
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

button {
  cursor: pointer;
  font-family: inherit;
  border: none;
  background: none;
  color: inherit;
}

input {
  font-family: inherit;
  color: inherit;
}

/* 自定义滚动条 */
::-webkit-scrollbar {
  width: 6px;
  height: 6px;
}
::-webkit-scrollbar-track {
  background: transparent;
}
::-webkit-scrollbar-thumb {
  background: var(--border-color-hover);
  border-radius: var(--radius-full);
}
::-webkit-scrollbar-thumb:hover {
  background: var(--text-muted);
}

/* ==========================================================================
   3. 顶部导航区 (Header)
   ========================================================================== */
.app-header {
  position: sticky;
  top: 0;
  height: var(--header-height);
  background-color: hsla(var(--bg-surface), 0.8);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-color);
  z-index: 50;
  transition: all var(--transition-normal);
}

.header-container {
  max-width: 1440px;
  height: 100%;
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

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

.logo-icon {
  width: 28px;
  height: 28px;
  color: var(--primary);
  filter: drop-shadow(0 2px 4px var(--primary-alpha));
}

.logo-area h1 {
  font-size: 1.15rem;
  font-weight: 700;
  letter-spacing: -0.01em;
}

.version-tag {
  font-size: 0.75rem;
  font-weight: 600;
  background-color: var(--primary-light);
  color: var(--primary);
  padding: 2px 8px;
  border-radius: var(--radius-full);
  border: 1px solid var(--primary-alpha);
}

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

/* 模式切换胶囊组 */
.mode-tabs {
  display: flex;
  background-color: var(--bg-surface-hover);
  padding: 4px;
  border-radius: var(--radius-full);
  border: 1px solid var(--border-color);
}

.tab-btn {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px 16px;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-muted);
  border-radius: var(--radius-full);
  transition: all var(--transition-fast);
}

.tab-btn:hover {
  color: var(--text-main);
}

.tab-btn.active {
  background-color: var(--bg-surface);
  color: var(--primary);
  box-shadow: var(--shadow-sm);
}

/* 深浅色模式切换按钮 */
.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border-radius: var(--radius-full);
  background-color: var(--bg-surface-hover);
  border: 1px solid var(--border-color);
  color: var(--text-muted);
  transition: all var(--transition-fast);
}

.theme-toggle:hover {
  color: var(--primary);
  background-color: var(--bg-surface-active);
  transform: rotate(15deg);
}

/* 根据当前属性展示正确图标 */
[data-theme="dark"] .icon-moon { display: none; }
[data-theme="dark"] .icon-sun { display: block; }
:not([data-theme="dark"]) .icon-moon { display: block; }
:not([data-theme="dark"]) .icon-sun { display: none; }

/* ==========================================================================
   4. 主体视图区排版 (Main & Layout)
   ========================================================================== */
.app-main {
  min-height: calc(100vh - var(--header-height));
  padding: 24px;
}

.main-layout {
  max-width: 1440px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: 320px 1fr;
  gap: 24px;
  align-items: start;
}

/* 左侧边控制台 */
.control-panel {
  display: flex;
  flex-direction: column;
  gap: 20px;
  position: sticky;
  top: calc(var(--header-height) + 24px);
  max-height: calc(100vh - var(--header-height) - 48px);
  overflow-y: auto;
  padding-right: 4px;
}

.panel-section {
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 18px;
  box-shadow: var(--shadow-sm);
  transition: all var(--transition-normal);
}

.panel-section h2 {
  font-size: 0.85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
  margin-bottom: 12px;
}

/* 搜索框 */
.search-box {
  position: relative;
  display: flex;
  align-items: center;
}

.search-box svg {
  position: absolute;
  left: 12px;
  color: var(--text-muted);
}

.search-box input {
  width: 100%;
  padding: 10px 32px 10px 36px;
  font-size: 0.875rem;
  background-color: var(--bg-surface-hover);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  outline: none;
  transition: all var(--transition-fast);
}

.search-box input:focus {
  background-color: var(--bg-surface);
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-light);
}

.clear-btn {
  position: absolute;
  right: 8px;
  width: 20px;
  height: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1rem;
  color: var(--text-muted);
  border-radius: var(--radius-full);
}
.clear-btn:hover {
  color: var(--text-main);
  background-color: var(--border-color);
}

/* 筛选芯片组 */
.filter-options {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 16px;
}
.filter-options:last-child { margin-bottom: 0; }

.filter-chip {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 12px;
  font-size: 0.8125rem;
  font-weight: 500;
  background-color: var(--bg-surface-hover);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  transition: all var(--transition-fast);
}

.filter-chip:hover {
  color: var(--text-main);
  border-color: var(--border-color-hover);
  background-color: var(--bg-surface-active);
}

.filter-chip.active {
  background-color: var(--primary-light);
  border-color: var(--primary);
  color: var(--primary);
  font-weight: 600;
}

.badge {
  font-size: 0.65rem;
  padding: 1px 6px;
  border-radius: var(--radius-full);
  font-weight: 700;
}

.wrong-badge {
  background-color: var(--danger-light);
  color: var(--danger);
  border: 1px solid hsla(var(--hue-danger), 84%, 60%, 0.2);
}

/* 进度统计总览 */
.stats-overview {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: 14px;
  border-top: 1px solid var(--border-color);
  margin-top: 4px;
}

.stat-item {
  display: flex;
  flex-direction: column;
}

.stat-label {
  font-size: 0.7rem;
  color: var(--text-muted);
  font-weight: 500;
}

.stat-val {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text-main);
}

/* 模拟考试控制区 */
.timer-display {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--primary);
  background-color: var(--primary-light);
  padding: 12px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--primary-alpha);
  margin-bottom: 12px;
  font-variant-numeric: tabular-nums;
}

/* 实时考试数据统计胶囊条 */
.exam-stats-bar {
  display: flex;
  align-items: center;
  justify-content: space-around;
  background-color: var(--bg-surface-hover);
  padding: 8px 12px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  margin-bottom: 12px;
}

.e-stat-pill {
  display: flex;
  align-items: baseline;
  gap: 6px;
}

.e-stat-lbl {
  font-size: 0.75rem;
  color: var(--text-muted);
}

.e-stat-val {
  font-size: 1.05rem;
  font-weight: 700;
}

.e-stat-val.done { color: var(--primary); }
.e-stat-val.remain { color: var(--warning); }

/* 答题卡小方格面板 */
.grid-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 12px;
}

.legend-hint {
  font-size: 0.7rem;
  color: var(--text-muted);
}

.question-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(32px, 1fr));
  gap: 6px;
  max-height: 220px;
  overflow-y: auto;
  padding-right: 4px;
}

.grid-cell {
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.75rem;
  font-weight: 600;
  border-radius: 4px;
  background-color: var(--bg-surface-hover);
  border: 1px solid var(--border-color);
  color: var(--text-muted);
  transition: all var(--transition-fast);
  user-select: none;
}

.grid-cell:hover {
  border-color: var(--primary);
  color: var(--text-main);
  transform: scale(1.1);
  z-index: 2;
}

.grid-cell.active {
  background-color: var(--primary);
  color: var(--text-inverse);
  border-color: var(--primary);
  box-shadow: 0 0 0 2px var(--primary-light);
}

.grid-cell.done-correct {
  background-color: var(--success-light);
  color: var(--success);
  border-color: hsla(var(--hue-success), 71%, 45%, 0.3);
}

.grid-cell.done-wrong {
  background-color: var(--danger-light);
  color: var(--danger);
  border-color: hsla(var(--hue-danger), 84%, 60%, 0.3);
}

/* ==========================================================================
   5. 核心答题工作台区 (Workbench & Cards)
   ========================================================================== */
.question-workbench {
  display: flex;
  flex-direction: column;
}

/* 加载态与空态 */
.loading-state, .empty-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 400px;
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  text-align: center;
  padding: 32px;
}

.spinner {
  width: 40px;
  height: 40px;
  border: 3px solid var(--border-color-hover);
  border-top-color: var(--primary);
  border-radius: var(--radius-full);
  animation: spin 0.8s linear infinite;
  margin-bottom: 16px;
}

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

.empty-state svg {
  color: var(--text-muted);
  margin-bottom: 16px;
}
.empty-state h3 { font-size: 1.25rem; margin-bottom: 8px; }
.empty-state p { color: var(--text-muted); font-size: 0.875rem; margin-bottom: 20px; }

/* 核心考题卡片 */
.question-card {
  display: flex;
  flex-direction: column;
  min-height: 520px; /* 设定优雅最小高度，避免切题时卡片伸缩导致底部按钮跳动 */
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  overflow: hidden;
  transition: all var(--transition-normal);
  animation: fadeIn var(--transition-normal);
}

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

.card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 28px;
  border-bottom: 1px solid var(--border-color);
  background-color: var(--bg-surface-hover);
}

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

.q-type-badge {
  font-size: 0.75rem;
  font-weight: 700;
  padding: 3px 10px;
  border-radius: var(--radius-sm);
  background-color: var(--primary);
  color: var(--text-inverse);
  letter-spacing: 0.05em;
}

.q-id {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-muted);
}

.btn-star {
  color: var(--border-color-hover);
  transition: all var(--transition-fast);
}
.btn-star:hover {
  color: var(--warning);
  transform: scale(1.15);
}
.btn-star.starred {
  color: var(--warning);
  fill: var(--warning);
}

/* 题面 */
.q-body {
  padding: 28px;
}

.q-title {
  font-size: 1.25rem;
  font-weight: 600;
  line-height: 1.5;
  letter-spacing: -0.01em;
}

/* 选项列表 */
.q-options {
  padding: 0 28px 28px;
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.opt-item {
  display: flex;
  align-items: flex-start;
  gap: 16px;
  padding: 16px 20px;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  background-color: var(--bg-surface);
  transition: all var(--transition-fast);
  user-select: none;
}

.opt-item:hover:not(.disabled) {
  border-color: var(--primary);
  background-color: var(--bg-surface-hover);
  transform: translateX(4px);
}

.opt-key {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  width: 28px;
  height: 28px;
  font-size: 0.875rem;
  font-weight: 700;
  border-radius: var(--radius-sm);
  background-color: var(--bg-surface-hover);
  border: 1px solid var(--border-color);
  color: var(--text-muted);
  transition: all var(--transition-fast);
}

.opt-text {
  font-size: 0.95rem;
  line-height: 1.5;
  padding-top: 2px;
}

/* 选项选中与判卷状态反馈 */
.opt-item.selected {
  border-color: var(--primary);
  background-color: var(--primary-light);
}
.opt-item.selected .opt-key {
  background-color: var(--primary);
  color: var(--text-inverse);
  border-color: var(--primary);
}

.opt-item.correct {
  border-color: var(--success);
  background-color: var(--success-light);
}
.opt-item.correct .opt-key {
  background-color: var(--success);
  color: var(--text-inverse);
  border-color: var(--success);
}

.opt-item.wrong {
  border-color: var(--danger);
  background-color: var(--danger-light);
}
.opt-item.wrong .opt-key {
  background-color: var(--danger);
  color: var(--text-inverse);
  border-color: var(--danger);
}

.opt-item.disabled {
  cursor: default;
  opacity: 0.9;
}

/* 多选题提交按钮区 */
.multiple-confirm-area {
  padding: 0 28px 20px;
  display: flex;
  justify-content: flex-end;
}

/* 答案解析反馈条 */
.q-feedback {
  margin: 0 28px 28px;
  border-radius: var(--radius-md);
  overflow: hidden;
  border: 1px solid var(--border-color);
  animation: expandDown var(--transition-normal);
}

@keyframes expandDown {
  from { opacity: 0; transform: scaleY(0.95); transform-origin: top; }
  to { opacity: 1; transform: scaleY(1); transform-origin: top; }
}

.feedback-banner {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 12px 20px;
  font-weight: 600;
  font-size: 0.95rem;
}
.feedback-banner.success {
  background-color: var(--success-light);
  color: var(--success);
}
.feedback-banner.danger {
  background-color: var(--danger-light);
  color: var(--danger);
}

.answer-detail {
  padding: 16px 20px;
  background-color: var(--bg-surface-hover);
  border-top: 1px solid var(--border-color);
  font-size: 0.95rem;
}

.ans-label { color: var(--text-muted); }
.ans-correct-val { font-size: 1.1rem; color: var(--success); font-weight: 700; letter-spacing: 0.05em; }

/* 底部切题栏 */
.card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 28px;
  background-color: var(--bg-surface-hover);
  border-top: 1px solid var(--border-color);
  margin-top: auto; /* 核心技巧：自动吸收剩余垂直空间，将导航栏稳稳压在卡片最底端 */
}

.btn-nav {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 10px 20px;
  font-size: 0.875rem;
  font-weight: 600;
  border-radius: var(--radius-sm);
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  transition: all var(--transition-fast);
}

.btn-nav:hover:not(:disabled) {
  border-color: var(--primary);
  color: var(--primary);
  background-color: var(--primary-light);
}

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

/* ==========================================================================
   6. 通用按钮组件 (Buttons)
   ========================================================================== */
.btn-primary {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 24px;
  font-size: 0.875rem;
  font-weight: 600;
  background-color: var(--primary);
  color: var(--text-inverse);
  border-radius: var(--radius-sm);
  box-shadow: var(--shadow-sm);
  transition: all var(--transition-fast);
}
.btn-primary:hover {
  background-color: var(--primary-hover);
  box-shadow: var(--shadow-md);
}

.btn-secondary {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 24px;
  font-size: 0.875rem;
  font-weight: 600;
  background-color: var(--bg-surface-hover);
  color: var(--text-main);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  transition: all var(--transition-fast);
}
.btn-secondary:hover {
  background-color: var(--border-color);
}

.btn-submit-exam {
  width: 100%;
  padding: 12px;
  font-size: 0.95rem;
}

/* ==========================================================================
   7. 弹窗层系统 (Modals - Glassmorphism)
   ========================================================================== */
.modal-overlay {
  position: fixed;
  inset: 0;
  background-color: hsla(0, 0%, 0%, 0.4);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px;
  animation: fadeIn var(--transition-fast);
}

.modal-container {
  width: 100%;
  max-width: 540px;
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-glass);
  overflow: hidden;
  animation: scaleUp var(--transition-normal);
}

@keyframes scaleUp {
  from { transform: scale(0.95); opacity: 0; }
  to { transform: scale(1); opacity: 1; }
}

.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 24px;
  border-bottom: 1px solid var(--border-color);
}

.modal-header h2 { font-size: 1.15rem; font-weight: 700; }

.btn-close-modal {
  font-size: 1.5rem;
  color: var(--text-muted);
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-full);
}
.btn-close-modal:hover { background-color: var(--bg-surface-hover); color: var(--text-main); }

.modal-body {
  padding: 24px;
}

.score-banner {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
  padding: 24px;
  background-color: var(--bg-surface-hover);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  margin-bottom: 24px;
}

.score-circle {
  width: 96px;
  height: 96px;
  border-radius: var(--radius-full);
  background-color: var(--bg-surface);
  border: 4px solid var(--primary);
  display: flex;
  align-items: baseline;
  justify-content: center;
  box-shadow: var(--shadow-sm);
  padding-top: 24px;
}

.score-num { font-size: 2.25rem; font-weight: 800; color: var(--primary); line-height: 1; }
.score-unit { font-size: 1rem; font-weight: 600; color: var(--text-muted); margin-left: 2px; }

.score-banner h3 { font-size: 1.1rem; font-weight: 600; }

.exam-stat-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 12px;
  margin-bottom: 24px;
}

.stat-box {
  padding: 12px;
  background-color: var(--bg-surface-hover);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  display: flex;
  flex-direction: column;
  align-items: center;
}
.stat-box.correct strong { color: var(--success); }
.stat-box.wrong strong { color: var(--danger); }

.box-lbl { font-size: 0.75rem; color: var(--text-muted); margin-bottom: 4px; }
.stat-box strong { font-size: 1.1rem; font-weight: 700; }

.wrong-review-section h4 { font-size: 0.9rem; margin-bottom: 6px; }
.review-desc { font-size: 0.8125rem; color: var(--text-muted); }

.modal-footer {
  display: flex;
  justify-content: flex-end;
  gap: 12px;
  padding: 16px 24px;
  background-color: var(--bg-surface-hover);
  border-top: 1px solid var(--border-color);
}

/* 自定义质感确认提示框样式 */
.dialog-container {
  max-width: 380px;
}
.dialog-container .modal-header {
  padding: 16px 20px;
}
.dialog-container .modal-header h2 {
  font-size: 1.05rem;
  color: var(--text-main);
}
.dialog-body {
  padding: 20px;
}
.dialog-body p {
  font-size: 0.95rem;
  line-height: 1.5;
  color: var(--text-muted);
  margin: 0;
}
.dialog-container .modal-footer {
  padding: 12px 20px;
}

/* 移动端专属触发条默认桌面隐藏 */
.mobile-panel-header {
  display: none;
}

/* ==========================================================================
   8. 响应式布局断点适配 (Responsive Media Queries)
   ========================================================================== */
@media (max-width: 1024px) {
  .main-layout {
    grid-template-columns: 260px 1fr;
    gap: 16px;
  }
}

@media (max-width: 768px) {
  :root {
    --header-height: 48px;
  }

  /* 移动端顶栏极致紧凑化与小尺寸排版 */
  .header-container { padding: 0 10px; }
  .logo-area { gap: 6px; }
  .logo-icon { width: 20px; height: 20px; flex-shrink: 0; }
  /* 告别移动端长文本孤字换行，通过伪元素注入短小精炼的单行文案呈现 */
  .logo-area h1 { font-size: 0; }
  .logo-area h1::after { content: "练习系统"; font-size: 0.85rem; font-weight: 700; white-space: nowrap; color: var(--text-main); }
  .version-tag { display: none; }
  
  .header-controls { gap: 6px; }
  .mode-tabs { padding: 2px; }
  .tab-btn { padding: 4px 10px; font-size: 0.75rem; gap: 4px; }
  .tab-btn svg { width: 12px; height: 12px; }
  .theme-toggle { width: 32px; height: 32px; }
  .theme-toggle svg { width: 16px; height: 16px; }
  
  .app-main { padding: 16px; }
  .main-layout {
    grid-template-columns: 1fr;
  }
  
  .control-panel {
    position: static;
    max-height: none;
    gap: 0; /* 折叠态由包裹层内部管理留白 */
  }

  /* 移动端控制台折叠栏呈现 */
  .mobile-panel-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 14px 18px;
    background-color: var(--primary-light);
    border: 1px solid var(--primary-alpha);
    border-radius: var(--radius-md);
    color: var(--primary);
    font-weight: 600;
    font-size: 0.9rem;
    cursor: pointer;
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-fast);
    margin-bottom: 16px;
    user-select: none;
    -webkit-tap-highlight-color: transparent;
  }
  .mobile-panel-header:active {
    transform: scale(0.98);
  }
  .m-header-left, .m-header-right {
    display: flex;
    align-items: center;
    gap: 8px;
  }
  .m-stat {
    font-size: 0.75rem;
    color: var(--text-muted);
    font-weight: 500;
  }
  .m-chevron {
    transition: transform var(--transition-normal);
  }

  /* 折叠状态管理 */
  .control-panel.is-collapsed .panel-content-wrapper {
    display: none;
  }
  .control-panel:not(.is-collapsed) .m-chevron {
    transform: rotate(180deg);
  }
  /* 移动端展开时自动隐藏重复的大尺寸倒计时框，极致释放垂直视图空间 */
  .control-panel:not(.is-collapsed) .timer-display {
    display: none;
  }
  .panel-content-wrapper {
    display: flex;
    flex-direction: column;
    gap: 16px;
    margin-bottom: 20px;
    animation: expandDown var(--transition-normal);
  }
  
  .question-grid { max-height: 140px; }
  
  .question-card { min-height: 420px; }
  .card-header { padding: 16px 20px; }
  .q-body { padding: 20px; }
  .q-options { padding: 0 20px 20px; }
  .q-feedback { margin: 0 20px 20px; }
  .card-footer { padding: 12px 20px; }
}