/* ==========================================
   PPT闪光课堂 - 全站样式 style.css
   ========================================== */

/* ==========================================
   1. CSS 变量定义
   ========================================== */
:root {
  /* 主色调 */
  --primary:        #FF6B35;
  --primary-dark:   #E85A25;
  --primary-light:  #FF8C5A;
  --secondary:      #FFD23F;
  --secondary-dark: #E8BA2A;

  /* 功能色 */
  --success:  #2ED573;
  --error:    #FF4757;
  --warning:  #FFD23F;
  --info:     #5B8BF5;

  /* 文字色 */
  --text-dark:  #1A1A2E;
  --text-mid:   #444466;
  --text-light: #888AAA;

  /* 背景色 */
  --bg:         #F8F7FF;
  --bg-card:    #FFFFFF;
  --bg-hover:   #FFF5F0;

  /* 边框 */
  --border:       #FFE0CC;
  --border-light: #FFF0E8;

  /* 圆角 */
  --radius-sm:   8px;
  --radius-md:   16px;
  --radius-lg:   24px;
  --radius-pill: 50px;

  /* 阴影 */
  --shadow-sm: 0 2px 8px rgba(255,107,53,0.08);
  --shadow-md: 0 4px 16px rgba(255,107,53,0.12);
  --shadow-lg: 0 8px 32px rgba(255,107,53,0.18);

  /* 字体 */
  --font-main:  'Microsoft YaHei', '微软雅黑', 'PingFang SC', sans-serif;
  --font-mono:  'Courier New', Courier, monospace;

  /* 导航高度 */
  --nav-height: 68px;

  /* 过渡 */
  --transition: all 0.3s ease;
}

/* ==========================================
   2. CSS Reset & 基础
   ========================================== */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: var(--font-main);
  background: var(--bg);
  color: var(--text-dark);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

a {
  text-decoration: none;
  color: inherit;
  transition: var(--transition);
}

ul, ol {
  list-style: none;
}

img {
  max-width: 100%;
  display: block;
}

button {
  cursor: pointer;
  font-family: var(--font-main);
  border: none;
  outline: none;
}

input, textarea, select {
  font-family: var(--font-main);
  outline: none;
}

/* ==========================================
   3. 通用布局
   ========================================== */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 1.5rem;
}

.section {
  padding: 5rem 0;
}

/* Section 标题组 */
.section-header {
  text-align: center;
  max-width: 640px;
  margin: 0 auto;
}

.section-tag {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.3rem 1rem;
  background: linear-gradient(135deg, #FFF0E8, #FFFBF0);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-pill);
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--primary);
  margin-bottom: 1rem;
}

.section-title {
  font-size: 2rem;
  font-weight: 900;
  color: var(--text-dark);
  line-height: 1.3;
  margin-bottom: 0.8rem;
}

.section-title span {
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.section-desc {
  font-size: 0.95rem;
  color: var(--text-light);
  line-height: 1.8;
}

/* ==========================================
   4. 通用按钮
   ========================================== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  padding: 0.65rem 1.4rem;
  border-radius: var(--radius-pill);
  font-size: 0.9rem;
  font-weight: 700;
  font-family: var(--font-main);
  cursor: pointer;
  transition: var(--transition);
  border: none;
  text-decoration: none;
  white-space: nowrap;
  line-height: 1;
}

.btn-primary {
  background: linear-gradient(135deg, var(--primary), var(--primary-light));
  color: white;
  box-shadow: 0 3px 12px rgba(255,107,53,0.3);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(255,107,53,0.4);
  color: white;
}

.btn-primary:active {
  transform: translateY(0);
}

.btn-secondary {
  background: linear-gradient(135deg, var(--secondary), var(--secondary-dark));
  color: var(--text-dark);
  box-shadow: 0 3px 12px rgba(255,210,63,0.3);
}

.btn-secondary:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(255,210,63,0.4);
  color: var(--text-dark);
}

.btn-outline {
  background: transparent;
  color: var(--primary);
  border: 2px solid var(--primary);
}

.btn-outline:hover {
  background: var(--primary);
  color: white;
  transform: translateY(-2px);
}

.btn-ghost {
  background: transparent;
  color: var(--text-mid);
  border: 1.5px solid var(--border);
}

.btn-ghost:hover {
  background: var(--bg-hover);
  color: var(--primary);
  border-color: var(--primary);
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  transform: none !important;
}

/* ==========================================
   5. 导航栏
   ========================================== */
.navbar {
  position: sticky;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  height: var(--nav-height);
  background: white;
  border-bottom: 1.5px solid var(--border-light);
  box-shadow: 0 2px 10px rgba(255,107,53,0.10);
  display: flex;
  align-items: center;
  padding: 0 1.5rem;
  gap: 1.5rem;
}

/* Logo */
.nav-logo {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 1.15rem;
  font-weight: 900;
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  white-space: nowrap;
  flex-shrink: 0;
  text-decoration: none;
}

.logo-icon {
  font-size: 1.4rem;
  -webkit-text-fill-color: initial;
  animation: sparkle 2s ease-in-out infinite;
}

@keyframes sparkle {
  0%, 100% { transform: scale(1) rotate(0deg); }
  50%       { transform: scale(1.15) rotate(10deg); }
}

/* 导航菜单 */
.nav-menu {
  display: flex;
  align-items: center;
  gap: 0.2rem;
  flex: 1;
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-item {
  position: relative;
}

.nav-link {
  display: flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.5rem 0.8rem;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--text-mid);
  cursor: pointer;
  transition: var(--transition);
  white-space: nowrap;
  user-select: none;
}

.nav-link:hover,
.nav-link.active {
  color: var(--primary);
  background: var(--bg-hover);
}

/* 下拉菜单 */
.dropdown-menu {
  position: absolute;
  top: calc(100% + 8px);
  left: 50%;
  transform: translateX(-50%) translateY(-8px);
  background: white;
  border: 1.5px solid var(--border);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  min-width: 220px;
  padding: 0.6rem;
  opacity: 0;
  visibility: hidden;
  transition: all 0.25s ease;
  z-index: 100;
}

.nav-item.has-dropdown:hover .dropdown-menu {
  opacity: 1;
  visibility: visible;
  transform: translateX(-50%) translateY(0);
}

.dropdown-header {
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--text-light);
  padding: 0.3rem 0.6rem 0.3rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.dropdown-item {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.55rem 0.7rem;
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  color: var(--text-mid);
  transition: var(--transition);
  cursor: pointer;
}

.dropdown-item:hover {
  background: var(--bg-hover);
  color: var(--primary);
  padding-left: 1rem;
}

.item-icon {
  font-size: 1rem;
  flex-shrink: 0;
}

/* 汉堡菜单按钮 */
.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  cursor: pointer;
  padding: 0.4rem;
  border-radius: var(--radius-sm);
  transition: var(--transition);
}

.nav-toggle span {
  display: block;
  width: 24px;
  height: 2.5px;
  background: var(--text-mid);
  border-radius: 2px;
  transition: var(--transition);
}

.nav-toggle:hover span {
  background: var(--primary);
}

.nav-toggle.active span:nth-child(1) {
  transform: translateY(7.5px) rotate(45deg);
}
.nav-toggle.active span:nth-child(2) {
  opacity: 0;
  transform: scaleX(0);
}
.nav-toggle.active span:nth-child(3) {
  transform: translateY(-7.5px) rotate(-45deg);
}

/* ==========================================
   6. 用户信息弹窗
   ========================================== */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(26,26,46,0.6);
  backdrop-filter: blur(6px);
  z-index: 9000;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1rem;
  opacity: 0;
  visibility: hidden;
  transition: all 0.35s ease;
}

.modal-overlay.show {
  opacity: 1;
  visibility: visible;
}

.modal-box {
  background: white;
  border-radius: var(--radius-lg);
  padding: 2.5rem 2rem;
  max-width: 420px;
  width: 100%;
  box-shadow: 0 20px 60px rgba(255,107,53,0.2);
  transform: scale(0.9) translateY(20px);
  transition: all 0.35s ease;
  text-align: center;
  border: 2px solid var(--border-light);
}

.modal-overlay.show .modal-box {
  transform: scale(1) translateY(0);
}

.modal-icon {
  font-size: 3.5rem;
  margin-bottom: 0.8rem;
  animation: float 3s ease-in-out infinite;
}

.modal-title {
  font-size: 1.4rem;
  font-weight: 900;
  color: var(--text-dark);
  margin-bottom: 0.4rem;
}

.modal-subtitle {
  font-size: 0.9rem;
  color: var(--text-light);
  margin-bottom: 1.5rem;
}

.modal-form {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  text-align: left;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.form-label {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-mid);
}

.form-input {
  padding: 0.75rem 1rem;
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: 0.95rem;
  color: var(--text-dark);
  background: var(--bg);
  transition: var(--transition);
  width: 100%;
}

.form-input:focus {
  border-color: var(--primary);
  background: white;
  box-shadow: 0 0 0 3px rgba(255,107,53,0.12);
}

.form-input::placeholder {
  color: #CCC;
}

.btn-start {
  width: 100%;
  padding: 0.9rem;
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  color: white;
  border: none;
  border-radius: var(--radius-pill);
  font-size: 1rem;
  font-weight: 700;
  font-family: var(--font-main);
  cursor: pointer;
  transition: var(--transition);
  margin-top: 0.5rem;
  box-shadow: 0 4px 16px rgba(255,107,53,0.3);
}

.btn-start:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(255,107,53,0.4);
}

.btn-start:active {
  transform: translateY(0);
}

/* ==========================================
   7. 通用卡片
   ========================================== */
.card {
  background: white;
  border-radius: var(--radius-md);
  border: 1.5px solid var(--border);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
  transition: var(--transition);
}

.card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: var(--primary);
}

.course-card {
  background: white;
  border-radius: var(--radius-md);
  border: 1.5px solid var(--border);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
  transition: var(--transition);
}

.course-card:hover {
  transform: translateY(-6px);
  box-shadow: var(--shadow-lg);
}

/* ==========================================
   8. 知识点内容页样式
   ========================================== */
.lesson-page {
  padding-top: var(--nav-height);
  min-height: 100vh;
}

.lesson-header {
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  padding: 3rem 0 4rem;
  text-align: center;
  position: relative;
  overflow: hidden;
}

.lesson-header::before {
  content: '';
  position: absolute;
  top: -60px;
  right: -60px;
  width: 220px;
  height: 220px;
  background: rgba(255,255,255,0.08);
  border-radius: 50%;
}

.lesson-breadcrumb {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  font-size: 0.82rem;
  color: rgba(255,255,255,0.75);
  margin-bottom: 1rem;
  flex-wrap: wrap;
}

.lesson-breadcrumb a {
  color: rgba(255,255,255,0.75);
  transition: var(--transition);
}

.lesson-breadcrumb a:hover {
  color: white;
}

.lesson-title {
  font-size: 2rem;
  font-weight: 900;
  color: white;
  margin-bottom: 0.6rem;
  text-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.lesson-subtitle {
  font-size: 0.95rem;
  color: rgba(255,255,255,0.85);
}

.lesson-wave {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  line-height: 0;
}

.lesson-wave svg {
  width: 100%;
  height: 50px;
  display: block;
}

/* 正文内容区 */
.lesson-body {
  max-width: 860px;
  margin: 0 auto;
  padding: 3rem 1.5rem 5rem;
}

/* 知识点卡片 */
.knowledge-card {
  background: white;
  border-radius: var(--radius-md);
  border: 1.5px solid var(--border);
  padding: 1.8rem;
  margin-bottom: 2rem;
  box-shadow: var(--shadow-sm);
  transition: var(--transition);
}

.knowledge-card:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-md);
}

.knowledge-card-title {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text-dark);
  margin-bottom: 1rem;
  padding-bottom: 0.8rem;
  border-bottom: 2px dashed var(--border);
}

/* 提示框 */
.tip-box {
  display: flex;
  gap: 0.8rem;
  padding: 1rem 1.2rem;
  border-radius: var(--radius-sm);
  margin: 1rem 0;
  font-size: 0.9rem;
  line-height: 1.7;
  border-left: 4px solid;
}

.tip-box.info {
  background: #F0F5FF;
  border-color: var(--info);
  color: #2a4a9e;
}

.tip-box.success {
  background: #EAFFF5;
  border-color: var(--success);
  color: #1a6640;
}

.tip-box.warning {
  background: #FFF8E8;
  border-color: var(--warning);
  color: #7a5c00;
}

.tip-box.danger {
  background: #FFF0F1;
  border-color: var(--error);
  color: #8a1a22;
}

.tip-icon {
  font-size: 1.2rem;
  flex-shrink: 0;
  margin-top: 0.1rem;
}

/* 步骤列表 */
.step-list {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  counter-reset: step-counter;
}

.step-item {
  display: flex;
  gap: 1rem;
  align-items: flex-start;
  counter-increment: step-counter;
}

.step-num {
  width: 32px;
  height: 32px;
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-size: 0.85rem;
  font-weight: 700;
  flex-shrink: 0;
}

.step-content {
  flex: 1;
  padding-top: 0.2rem;
  font-size: 0.9rem;
  color: var(--text-mid);
  line-height: 1.7;
}

.step-content strong {
  color: var(--text-dark);
}

/* 对比表格 */
.compare-table {
  width: 100%;
  border-collapse: collapse;
  border-radius: var(--radius-sm);
  overflow: hidden;
  font-size: 0.875rem;
  margin: 1rem 0;
}

.compare-table th {
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  color: white;
  padding: 0.75rem 1rem;
  text-align: left;
  font-weight: 700;
}

.compare-table td {
  padding: 0.7rem 1rem;
  border-bottom: 1px solid var(--border-light);
  color: var(--text-mid);
  vertical-align: top;
}

.compare-table tr:nth-child(even) td {
  background: #FFFBF8;
}

.compare-table tr:hover td {
  background: var(--bg-hover);
}

/* 标签列表 */
.tag-list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin: 0.8rem 0;
}

.tag {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.3rem 0.8rem;
  background: linear-gradient(135deg, #FFF0E8, #FFFBF0);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-pill);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--primary);
}

/* 导航按钮（上一课/下一课） */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  margin-top: 3rem;
  padding-top: 2rem;
  border-top: 2px dashed var(--border);
  flex-wrap: wrap;
}

.lesson-nav-btn {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.7rem 1.2rem;
  background: white;
  border: 1.5px solid var(--border);
  border-radius: var(--radius-md);
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-mid);
  cursor: pointer;
  transition: var(--transition);
  text-decoration: none;
  flex: 1;
  min-width: 120px;
}

.lesson-nav-btn:hover {
  border-color: var(--primary);
  color: var(--primary);
  background: var(--bg-hover);
  transform: translateX(0) translateY(-2px);
}

.lesson-nav-btn.prev:hover { transform: translateX(-3px) translateY(-2px); }
.lesson-nav-btn.next:hover { transform: translateX(3px) translateY(-2px); }
.lesson-nav-btn.next { justify-content: flex-end; text-align: right; }
/* ==========================================
   9. 测验组件样式
   ========================================== */

/* 测验页面整体容器 */
.quiz-page {
  padding-top: var(--nav-height);
  min-height: 100vh;
  background: var(--bg);
}

/* 测验顶部 Banner */
.quiz-header {
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  padding: 2.5rem 0 3.5rem;
  text-align: center;
  position: relative;
  overflow: hidden;
}

.quiz-header::before {
  content: '📝';
  position: absolute;
  font-size: 8rem;
  top: -1.5rem;
  left: 3%;
  opacity: 0.08;
  transform: rotate(-15deg);
}

.quiz-header::after {
  content: '🏆';
  position: absolute;
  font-size: 8rem;
  bottom: -2rem;
  right: 3%;
  opacity: 0.08;
  transform: rotate(15deg);
}

.quiz-header-title {
  font-size: 1.8rem;
  font-weight: 900;
  color: white;
  margin-bottom: 0.5rem;
  text-shadow: 0 2px 8px rgba(0,0,0,0.1);
  position: relative;
  z-index: 1;
}

.quiz-header-sub {
  font-size: 0.9rem;
  color: rgba(255,255,255,0.85);
  position: relative;
  z-index: 1;
}

.quiz-header-wave {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  line-height: 0;
}

.quiz-header-wave svg {
  width: 100%;
  height: 40px;
  display: block;
}

/* 测验主体 */
.quiz-body {
  max-width: 720px;
  margin: 0 auto;
  padding: 2.5rem 1.5rem 5rem;
}

/* 进度条 */
.quiz-progress {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  margin-bottom: 1.5rem;
}

.quiz-progress-bar {
  flex: 1;
  height: 10px;
  background: white;
  border-radius: var(--radius-pill);
  overflow: hidden;
  border: 1.5px solid var(--border);
  box-shadow: inset 0 1px 3px rgba(0,0,0,0.05);
}

.quiz-progress-fill {
  height: 100%;
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  border-radius: var(--radius-pill);
  transition: width 0.5s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
}

.quiz-progress-fill::after {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: linear-gradient(
    90deg,
    transparent 0%,
    rgba(255,255,255,0.3) 50%,
    transparent 100%
  );
  animation: shimmer 1.5s infinite;
}

@keyframes shimmer {
  0%   { transform: translateX(-100%); }
  100% { transform: translateX(100%); }
}

.quiz-progress-text {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--text-mid);
  white-space: nowrap;
  min-width: 48px;
  text-align: right;
}

/* 题目卡片 */
.quiz-question-card {
  background: white;
  border-radius: var(--radius-md);
  border: 1.5px solid var(--border);
  padding: 1.8rem;
  margin-bottom: 1.2rem;
  box-shadow: var(--shadow-sm);
}

.quiz-type-badge {
  margin-bottom: 1rem;
}

.quiz-question-text {
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--text-dark);
  line-height: 1.7;
  margin-bottom: 1.5rem;
}

/* 答题区域 */
.quiz-answer-area {
  margin-bottom: 1rem;
}

/* ---- 单选题选项 ---- */
.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.quiz-option {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  padding: 0.85rem 1.1rem;
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: var(--transition);
  font-size: 0.95rem;
  color: var(--text-mid);
  user-select: none;
}

.quiz-option:hover {
  background: var(--bg-hover);
  border-color: var(--primary);
  color: var(--primary);
  transform: translateX(4px);
}

.quiz-option.selected {
  background: linear-gradient(135deg, #FFF0E8, #FFFBF0);
  border-color: var(--primary);
  color: var(--primary);
  font-weight: 600;
  transform: translateX(4px);
}

.quiz-option.correct {
  background: linear-gradient(135deg, #EAFFF5, #F0FFF8);
  border-color: var(--success);
  color: #1a6640;
  font-weight: 600;
}

.quiz-option.wrong {
  background: linear-gradient(135deg, #FFF0F1, #FFF5F5);
  border-color: var(--error);
  color: #8a1a22;
  font-weight: 600;
}

.quiz-option.disabled {
  cursor: not-allowed;
}

.option-letter {
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.8rem;
  font-weight: 700;
  flex-shrink: 0;
  transition: var(--transition);
}

.quiz-option.selected .option-letter {
  background: var(--primary);
  color: white;
}

.quiz-option.correct .option-letter {
  background: var(--success);
  color: white;
}

.quiz-option.wrong .option-letter {
  background: var(--error);
  color: white;
}

/* ---- 判断题 ---- */
.judge-options {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
}

.judge-option {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 1.5rem 1rem;
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: var(--transition);
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-mid);
  user-select: none;
}

.judge-option:hover {
  background: var(--bg-hover);
  border-color: var(--primary);
  color: var(--primary);
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
}

.judge-option.selected {
  background: linear-gradient(135deg, #FFF0E8, #FFFBF0);
  border-color: var(--primary);
  color: var(--primary);
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
}

.judge-option.correct {
  background: linear-gradient(135deg, #EAFFF5, #F0FFF8);
  border-color: var(--success);
  color: #1a6640;
}

.judge-option.wrong {
  background: linear-gradient(135deg, #FFF0F1, #FFF5F5);
  border-color: var(--error);
  color: #8a1a22;
}

.judge-icon {
  font-size: 2.5rem;
  line-height: 1;
}

/* ---- 连线题 ---- */
.match-container {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
}

.match-col {
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.match-item {
  padding: 0.7rem 1rem;
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: var(--transition);
  font-size: 0.9rem;
  color: var(--text-mid);
  text-align: center;
  user-select: none;
}

.match-item:hover {
  background: var(--bg-hover);
  border-color: var(--primary);
  color: var(--primary);
}

.match-item.selected {
  background: linear-gradient(135deg, #FFF0E8, #FFFBF0);
  border-color: var(--primary);
  color: var(--primary);
  font-weight: 600;
  box-shadow: 0 0 0 3px rgba(255,107,53,0.15);
}

.match-item.matched {
  background: linear-gradient(135deg, #EAFFF5, #F0FFF8);
  border-color: var(--success);
  color: #1a6640;
  font-weight: 600;
  cursor: default;
}

.match-item.wrong {
  background: linear-gradient(135deg, #FFF0F1, #FFF5F5);
  border-color: var(--error);
  color: #8a1a22;
}

/* ---- 答题反馈 ---- */
.quiz-feedback {
  display: none;
  align-items: flex-start;
  gap: 0.8rem;
  padding: 1rem 1.2rem;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  line-height: 1.7;
  margin-top: 1rem;
  border-left: 4px solid;
  animation: slideDown 0.3s ease;
}

.quiz-feedback.show {
  display: flex;
}

.quiz-feedback.correct {
  background: linear-gradient(135deg, #EAFFF5, #F5FFF9);
  border-color: var(--success);
  color: #1a6640;
}

.quiz-feedback.wrong {
  background: linear-gradient(135deg, #FFF0F1, #FFF5F5);
  border-color: var(--error);
  color: #7a2030;
}

@keyframes slideDown {
  from {
    opacity: 0;
    transform: translateY(-10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* ---- 测验结果页 ---- */
.quiz-result {
  background: white;
  border-radius: var(--radius-lg);
  border: 1.5px solid var(--border);
  padding: 3rem 2rem;
  text-align: center;
  box-shadow: var(--shadow-lg);
}

.quiz-result-icon {
  font-size: 5rem;
  margin-bottom: 1rem;
  animation: bounceIn 0.6s ease;
}

@keyframes bounceIn {
  0%   { transform: scale(0.3); opacity: 0; }
  50%  { transform: scale(1.1); opacity: 1; }
  70%  { transform: scale(0.95); }
  100% { transform: scale(1); }
}

.quiz-result-title {
  font-size: 1.4rem;
  font-weight: 900;
  color: var(--text-dark);
  margin-bottom: 0.5rem;
}

.quiz-result-score {
  font-size: 5rem;
  font-weight: 900;
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  line-height: 1.1;
  margin: 0.5rem 0;
}

.quiz-result-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.5rem 1.2rem;
  background: linear-gradient(135deg, #FFF8E0, #FFF0E0);
  border: 2px solid var(--secondary);
  border-radius: var(--radius-pill);
  font-size: 0.95rem;
  font-weight: 700;
  color: #b8860b;
  margin: 0.8rem 0;
}

.badge-icon {
  font-size: 1.3rem;
}

.quiz-result-encourage {
  font-size: 1rem;
  color: var(--text-mid);
  margin: 0.8rem 0 1.5rem;
  line-height: 1.7;
  font-style: italic;
}

/* 统计数据 */
.quiz-stats {
  display: flex;
  justify-content: center;
  gap: 0;
  margin: 1.5rem 0;
  background: var(--bg);
  border-radius: var(--radius-md);
  border: 1.5px solid var(--border);
  overflow: hidden;
}

.quiz-stat-item {
  flex: 1;
  padding: 1.2rem 0.5rem;
  border-right: 1.5px solid var(--border);
}

.quiz-stat-item:last-child {
  border-right: none;
}

.quiz-stat-num {
  font-size: 2rem;
  font-weight: 900;
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  line-height: 1.1;
}

.quiz-stat-label {
  font-size: 0.78rem;
  color: var(--text-light);
  margin-top: 0.3rem;
}

/* 结果页操作按钮组 */
.quiz-result-actions {
  display: flex;
  justify-content: center;
  gap: 0.8rem;
  flex-wrap: wrap;
  margin-top: 1.5rem;
}

/* ==========================================
   10. Toast 消息提示
   ========================================== */
.toast-container {
  position: fixed;
  top: calc(var(--nav-height) + 16px);
  right: 1rem;
  z-index: 9999;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  pointer-events: none;
}

.toast {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  padding: 0.75rem 1.1rem;
  background: white;
  border-radius: var(--radius-md);
  box-shadow: 0 4px 20px rgba(0,0,0,0.12);
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-dark);
  border-left: 4px solid var(--primary);
  animation: toastIn 0.3s ease;
  pointer-events: auto;
  max-width: 320px;
  min-width: 200px;
}

.toast.success { border-color: var(--success); }
.toast.error   { border-color: var(--error);   }
.toast.warning { border-color: var(--warning);  }
.toast.info    { border-color: var(--info);     }

.toast.out {
  animation: toastOut 0.3s ease forwards;
}

@keyframes toastIn {
  from {
    opacity: 0;
    transform: translateX(100%);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes toastOut {
  from {
    opacity: 1;
    transform: translateX(0);
  }
  to {
    opacity: 0;
    transform: translateX(110%);
  }
}

/* ==========================================
   11. 页脚
   ========================================== */
.footer {
  background: linear-gradient(135deg, #1A1A2E, #16213E);
  color: rgba(255,255,255,0.85);
  padding: 3.5rem 0 0;
}

.footer-top {
  display: grid;
  grid-template-columns: 2fr 1.2fr 1.2fr;
  gap: 3rem;
  padding-bottom: 2.5rem;
  border-bottom: 1px solid rgba(255,255,255,0.08);
}

.footer-brand .nav-logo {
  -webkit-text-fill-color: white;
  color: white;
  background: none;
  margin-bottom: 1rem;
  display: inline-flex;
}

.footer-desc {
  font-size: 0.875rem;
  color: rgba(255,255,255,0.55);
  line-height: 1.8;
}

.footer-col-title {
  font-size: 0.85rem;
  font-weight: 700;
  color: rgba(255,255,255,0.9);
  margin-bottom: 0.8rem;
  letter-spacing: 0.03em;
}

.footer-links {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.footer-links a {
  font-size: 0.85rem;
  color: rgba(255,255,255,0.5);
  transition: var(--transition);
  display: flex;
  align-items: center;
  gap: 0.3rem;
}

.footer-links a:hover {
  color: var(--secondary);
  transform: translateX(4px);
}

.footer-bottom {
  padding: 1.2rem 0;
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 0.8rem;
  color: rgba(255,255,255,0.35);
  flex-wrap: wrap;
  gap: 0.5rem;
}

/* ==========================================
   12. 动画类
   ========================================== */

/* 浮动动画 */
@keyframes float {
  0%, 100% { transform: translateY(0px); }
  50%       { transform: translateY(-10px); }
}

/* 淡入上升 */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(30px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* 淡入 */
@keyframes fadeIn {
  from { opacity: 0; }
  to   { opacity: 1; }
}

/* 左滑入 */
@keyframes slideInLeft {
  from {
    opacity: 0;
    transform: translateX(-30px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

/* 右滑入 */
@keyframes slideInRight {
  from {
    opacity: 0;
    transform: translateX(30px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

/* 缩放入场 */
@keyframes scaleIn {
  from {
    opacity: 0;
    transform: scale(0.85);
  }
  to {
    opacity: 1;
    transform: scale(1);
  }
}

/* 动画工具类 */
.fade-in {
  animation: fadeInUp 0.6s ease both;
}

.fade-in-delay-1 { animation-delay: 0.1s; }
.fade-in-delay-2 { animation-delay: 0.2s; }
.fade-in-delay-3 { animation-delay: 0.3s; }
.fade-in-delay-4 { animation-delay: 0.4s; }

.slide-left  { animation: slideInLeft  0.6s ease both; }
.slide-right { animation: slideInRight 0.6s ease both; }
.scale-in    { animation: scaleIn      0.5s ease both; }

/* Intersection Observer 触发动画 */
.animate-on-scroll {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.animate-on-scroll.visible {
  opacity: 1;
  transform: translateY(0);
}

/* ==========================================
   13. 工具类
   ========================================== */
.text-center  { text-align: center; }
.text-left    { text-align: left; }
.text-right   { text-align: right; }
.text-primary { color: var(--primary); }
.text-success { color: var(--success); }
.text-error   { color: var(--error); }
.text-light   { color: var(--text-light); }

.fw-700 { font-weight: 700; }
.fw-900 { font-weight: 900; }

.mt-1 { margin-top: 0.5rem;  }
.mt-2 { margin-top: 1rem;    }
.mt-3 { margin-top: 1.5rem;  }
.mt-4 { margin-top: 2rem;    }
.mb-1 { margin-bottom: 0.5rem; }
.mb-2 { margin-bottom: 1rem;   }
.mb-3 { margin-bottom: 1.5rem; }
.mb-4 { margin-bottom: 2rem;   }

.d-flex        { display: flex; }
.align-center  { align-items: center; }
.justify-center{ justify-content: center; }
.gap-1         { gap: 0.5rem; }
.gap-2         { gap: 1rem;   }
.flex-wrap     { flex-wrap: wrap; }

.hidden  { display: none !important; }
.visible { visibility: visible; }

/* ==========================================
   14. 滚动条美化
   ========================================== */
::-webkit-scrollbar {
  width: 6px;
  height: 6px;
}

::-webkit-scrollbar-track {
  background: var(--bg);
}

::-webkit-scrollbar-thumb {
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  border-radius: 3px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--primary-dark);
}

/* ==========================================
   15. 选中文字样式
   ========================================== */
::selection {
  background: rgba(255,107,53,0.2);
  color: var(--primary-dark);
}

/* ==========================================
   16. 响应式断点
   ========================================== */

/* 平板 ≤ 1024px */
@media (max-width: 1024px) {
  .container {
    max-width: 100%;
    padding: 0 1.2rem;
  }

  .nav-menu {
    gap: 0;
  }

  .nav-link {
    padding: 0.5rem 0.6rem;
    font-size: 0.85rem;
  }

  .footer-top {
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
  }

  .footer-brand {
    grid-column: 1 / -1;
  }
}

/* 移动端 ≤ 768px */
@media (max-width: 768px) {

  /* 导航变为汉堡菜单 */
  .nav-menu {
    display: none;
    position: fixed;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background: white;
    border-bottom: 1.5px solid var(--border);
    box-shadow: var(--shadow-lg);
    flex-direction: column;
    align-items: stretch;
    padding: 1rem;
    gap: 0.3rem;
    z-index: 999;
    max-height: calc(100vh - var(--nav-height));
    overflow-y: auto;
  }

  .nav-menu.open {
    display: flex;
    animation: slideDown 0.3s ease;
  }

  .nav-toggle {
    display: flex;
  }

  .has-dropdown .dropdown-menu {
    position: static;
    transform: none;
    opacity: 1;
    visibility: visible;
    box-shadow: none;
    border: none;
    background: var(--bg);
    border-radius: var(--radius-sm);
    padding: 0.4rem;
    display: none;
  }

  .has-dropdown.open .dropdown-menu {
    display: block;
  }

  .nav-link {
    width: 100%;
    padding: 0.7rem 0.8rem;
    border-radius: var(--radius-sm);
    font-size: 0.95rem;
  }

  /* 测验页面 */
  .quiz-body {
    padding: 1.5rem 1rem 4rem;
  }

  .quiz-question-card {
    padding: 1.2rem;
  }

  .quiz-question-text {
    font-size: 0.95rem;
  }

  .judge-options {
    grid-template-columns: 1fr 1fr;
    gap: 0.8rem;
  }

  .judge-icon {
    font-size: 2rem;
  }

  .match-container {
    gap: 0.8rem;
  }

  .match-item {
    padding: 0.6rem 0.5rem;
    font-size: 0.82rem;
  }

  .quiz-result {
    padding: 2rem 1.2rem;
  }

  .quiz-result-score {
    font-size: 4rem;
  }

  .quiz-stats {
    flex-direction: row;
  }

  .quiz-stat-num {
    font-size: 1.6rem;
  }

  .quiz-result-actions {
    flex-direction: column;
    align-items: stretch;
  }

  .quiz-result-actions .btn,
  .quiz-result-actions a {
    text-align: center;
    justify-content: center;
  }

  /* 知识页 */
  .lesson-title {
    font-size: 1.5rem;
  }

  .lesson-body {
    padding: 2rem 1rem 4rem;
  }

  .knowledge-card {
    padding: 1.2rem;
  }

  .compare-table {
    font-size: 0.8rem;
    display: block;
    overflow-x: auto;
  }

  .lesson-nav {
    flex-direction: column;
  }

  .lesson-nav-btn {
    width: 100%;
    justify-content: center !important;
    text-align: center !important;
  }

  /* 页脚 */
  .footer-top {
    grid-template-columns: 1fr;
    gap: 1.5rem;
  }

  .footer-bottom {
    flex-direction: column;
    text-align: center;
    gap: 0.3rem;
  }

  /* Section标题 */
  .section-title {
    font-size: 1.5rem;
  }
}

/* 小屏手机 ≤ 480px */
@media (max-width: 480px) {
  html { font-size: 15px; }

  .container {
    padding: 0 0.9rem;
  }

  .navbar {
    padding: 0 0.9rem;
  }

  .quiz-header-title {
    font-size: 1.4rem;
  }

  .judge-options {
    grid-template-columns: 1fr 1fr;
  }

  .judge-option {
    padding: 1rem 0.5rem;
  }

  .match-container {
    grid-template-columns: 1fr 1fr;
  }

  .quiz-stats {
    flex-direction: row;
    flex-wrap: wrap;
  }

  .quiz-stat-item {
    flex: 1 0 30%;
    border-right: 1.5px solid var(--border);
    border-bottom: 1.5px solid var(--border);
  }

  .quiz-stat-item:last-child {
    border-bottom: none;
  }

  .toast {
    max-width: calc(100vw - 2rem);
    font-size: 0.82rem;
  }

  .modal-box {
    padding: 2rem 1.2rem;
  }

  .modal-title {
    font-size: 1.2rem;
  }
}

/* 超大屏 ≥ 1400px */
@media (min-width: 1400px) {
  .container {
    max-width: 1320px;
  }
}

/* ==========================================
   17. 打印样式
   ========================================== */
@media print {
  .navbar,
  .footer,
  .quiz-result-actions,
  .lesson-nav,
  .modal-overlay,
  .toast-container {
    display: none !important;
  }

  body {
    background: white;
    color: black;
  }

  .lesson-body,
  .quiz-body {
    padding: 0;
    max-width: 100%;
  }

 .knowledge-card,
 .quiz-question-card {
    box-shadow: none;
    border: 1px solid #ccc;
    page-break-inside: avoid;
  }

  .tip-box {
    border: 1px solid #ccc;
  }

  a::after {
    content: none;
  }
}