/* ===== 小学奥数在线学习站 - 全局样式 ===== */
:root {
  --primary: #4361ee;
  --primary-light: #eef2ff;
  --primary-dark: #3730a3;
  --accent: #f59e0b;
  --accent-light: #fef3c7;
  --success: #10b981;
  --success-light: #d1fae5;
  --danger: #ef4444;
  --danger-light: #fee2e2;
  --text: #1e293b;
  --text-light: #64748b;
  --bg: #f8fafc;
  --card-bg: #ffffff;
  --border: #e2e8f0;
  --radius: 12px;
  --shadow: 0 4px 6px -1px rgba(0,0,0,0.07), 0 2px 4px -2px rgba(0,0,0,0.05);
  --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.08), 0 4px 6px -4px rgba(0,0,0,0.04);
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --grade1: #ef4444;
  --grade2: #f97316;
  --grade3: #eab308;
  --grade4: #22c55e;
  --grade5: #3b82f6;
  --grade6: #8b5cf6;
}

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

body {
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  font-size: 16px;
}

a { color: var(--primary); text-decoration: none; transition: color .2s; }
a:hover { color: var(--primary-dark); }

/* ===== 顶部导航 ===== */
.site-header {
  background: var(--card-bg);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: 0 1px 3px rgba(0,0,0,0.05);
}
.header-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 24px;
  height: 64px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.logo {
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--primary);
  display: flex;
  align-items: center;
  gap: 8px;
}
.logo-icon { font-size: 1.5rem; }
.nav-links { display: flex; gap: 8px; flex-wrap: wrap; }
.nav-links a {
  padding: 6px 14px;
  border-radius: 20px;
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--text-light);
  transition: all .2s;
}
.nav-links a:hover, .nav-links a.active {
  background: var(--primary-light);
  color: var(--primary);
}

/* ===== 通用容器 ===== */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 32px 24px;
}

/* ===== 首页 Hero ===== */
.hero {
  text-align: center;
  padding: 60px 24px 48px;
  background: linear-gradient(135deg, var(--primary-light) 0%, #f0f9ff 100%);
  border-bottom: 1px solid var(--border);
}
.hero h1 {
  font-size: 2.4rem;
  font-weight: 800;
  margin-bottom: 12px;
  color: var(--primary-dark);
}
.hero p {
  font-size: 1.1rem;
  color: var(--text-light);
  max-width: 600px;
  margin: 0 auto;
}

/* ===== 年级卡片网格 ===== */
.grade-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 24px;
  margin-top: 32px;
}
.grade-card {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 28px;
  box-shadow: var(--shadow);
  border-top: 4px solid var(--primary);
  transition: transform .2s, box-shadow .2s;
  display: block;
  color: var(--text);
}
.grade-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  color: var(--text);
}
.grade-card h3 { font-size: 1.2rem; margin-bottom: 8px; }
.grade-card p { font-size: 0.9rem; color: var(--text-light); margin-bottom: 12px; }
.grade-card .topic-count {
  display: inline-block;
  font-size: 0.8rem;
  background: var(--primary-light);
  color: var(--primary);
  padding: 3px 10px;
  border-radius: 12px;
  font-weight: 500;
}
.grade-card[data-grade="1"] { border-top-color: var(--grade1); }
.grade-card[data-grade="2"] { border-top-color: var(--grade2); }
.grade-card[data-grade="3"] { border-top-color: var(--grade3); }
.grade-card[data-grade="4"] { border-top-color: var(--grade4); }
.grade-card[data-grade="5"] { border-top-color: var(--grade5); }
.grade-card[data-grade="6"] { border-top-color: var(--grade6); }

/* ===== 年级页面布局 ===== */
.grade-layout {
  display: grid;
  grid-template-columns: 260px 1fr;
  gap: 32px;
  align-items: start;
}
@media (max-width: 900px) {
  .grade-layout { grid-template-columns: 1fr; }
  .sidebar { position: static !important; }
}

/* 侧边栏 */
.sidebar {
  position: sticky;
  top: 80px;
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 20px;
  box-shadow: var(--shadow);
  max-height: calc(100vh - 100px);
  overflow-y: auto;
}
.sidebar h3 {
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--text-light);
  margin-bottom: 12px;
}
.sidebar ul { list-style: none; }
.sidebar li { margin-bottom: 4px; }
.sidebar a {
  display: block;
  padding: 8px 12px;
  border-radius: 8px;
  font-size: 0.9rem;
  color: var(--text);
  transition: all .15s;
}
.sidebar a:hover, .sidebar a.active {
  background: var(--primary-light);
  color: var(--primary);
}
.sidebar .progress-bar {
  margin-top: 16px;
  padding-top: 16px;
  border-top: 1px solid var(--border);
}
.progress-track {
  height: 8px;
  background: var(--border);
  border-radius: 4px;
  overflow: hidden;
  margin-top: 6px;
}
.progress-fill {
  height: 100%;
  background: var(--success);
  border-radius: 4px;
  transition: width .4s ease;
}
.progress-text { font-size: 0.8rem; color: var(--text-light); }

/* ===== 专题内容区 ===== */
.topic-section {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 32px;
  margin-bottom: 24px;
  box-shadow: var(--shadow);
}
.topic-section h2 {
  font-size: 1.5rem;
  margin-bottom: 8px;
  padding-bottom: 12px;
  border-bottom: 2px solid var(--primary-light);
}
.topic-section h3 {
  font-size: 1.15rem;
  margin: 24px 0 12px;
  color: var(--primary-dark);
}
.topic-section h4 {
  font-size: 1rem;
  margin: 16px 0 8px;
}

/* 知识点框 */
.knowledge-box {
  background: var(--primary-light);
  border-left: 4px solid var(--primary);
  border-radius: 0 8px 8px 0;
  padding: 16px 20px;
  margin: 16px 0;
}
.knowledge-box .kb-title {
  font-weight: 700;
  font-size: 0.9rem;
  color: var(--primary);
  margin-bottom: 8px;
}

/* 例题框 */
.example-box {
  background: #fffbeb;
  border: 1px solid #fde68a;
  border-radius: 8px;
  padding: 20px;
  margin: 16px 0;
}
.example-box .ex-label {
  font-weight: 700;
  font-size: 0.85rem;
  color: #d97706;
  margin-bottom: 8px;
}
.example-box .ex-question { margin-bottom: 12px; font-weight: 500; }
.example-box .ex-solution {
  background: rgba(255,255,255,0.7);
  border-radius: 6px;
  padding: 12px 16px;
  font-size: 0.92rem;
  line-height: 1.8;
}
.example-box .ex-solution summary {
  cursor: pointer;
  font-weight: 600;
  color: #92400e;
}

/* 公式 */
.formula {
  text-align: center;
  font-size: 1.1rem;
  font-weight: 600;
  padding: 12px;
  background: #f1f5f9;
  border-radius: 8px;
  margin: 12px 0;
  font-family: "Times New Roman", serif;
}

/* ===== 练习题区 ===== */
.quiz-area {
  margin-top: 24px;
  padding-top: 20px;
  border-top: 2px dashed var(--border);
}
.quiz-area h3 {
  color: var(--success);
  margin-bottom: 16px;
}
.quiz-item {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 16px 20px;
  margin-bottom: 12px;
}
.quiz-item .q-text { font-weight: 500; margin-bottom: 10px; }
.quiz-options { display: flex; flex-direction: column; gap: 8px; }
.quiz-options label {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 12px;
  border-radius: 6px;
  border: 1px solid var(--border);
  cursor: pointer;
  transition: all .15s;
  font-size: 0.92rem;
}
.quiz-options label:hover { background: var(--primary-light); border-color: var(--primary); }
.quiz-options input[type="radio"] { accent-color: var(--primary); }

/* 填空题 */
.fill-input {
  border: 2px solid var(--border);
  border-radius: 6px;
  padding: 8px 12px;
  font-size: 1rem;
  width: 120px;
  text-align: center;
  transition: border-color .2s;
}
.fill-input:focus { outline: none; border-color: var(--primary); }
.fill-input.correct { border-color: var(--success); background: var(--success-light); }
.fill-input.wrong { border-color: var(--danger); background: var(--danger-light); }

/* 提交与反馈 */
.quiz-submit {
  display: inline-block;
  margin-top: 12px;
  padding: 10px 24px;
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: 8px;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: background .2s;
}
.quiz-submit:hover { background: var(--primary-dark); }
.quiz-feedback {
  margin-top: 10px;
  padding: 10px 16px;
  border-radius: 6px;
  font-size: 0.9rem;
  display: none;
}
.quiz-feedback.show { display: block; }
.quiz-feedback.correct { background: var(--success-light); color: #065f46; }
.quiz-feedback.wrong { background: var(--danger-light); color: #991b1b; }

/* ===== 页脚 ===== */
.site-footer {
  text-align: center;
  padding: 32px 24px;
  color: var(--text-light);
  font-size: 0.85rem;
  border-top: 1px solid var(--border);
  margin-top: 48px;
}

/* ===== 面包屑 ===== */
.breadcrumb {
  font-size: 0.85rem;
  color: var(--text-light);
  margin-bottom: 20px;
}
.breadcrumb a { color: var(--text-light); }
.breadcrumb a:hover { color: var(--primary); }

/* ===== 标签 ===== */
.tag {
  display: inline-block;
  font-size: 0.75rem;
  padding: 2px 8px;
  border-radius: 4px;
  font-weight: 500;
  margin-right: 6px;
}
.tag-basic { background: var(--success-light); color: #065f46; }
.tag-medium { background: var(--accent-light); color: #92400e; }
.tag-hard { background: var(--danger-light); color: #991b1b; }

/* ===== 学习路线图 ===== */
.roadmap {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  margin: 24px 0;
}
.roadmap-step {
  flex: 1;
  min-width: 160px;
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 20px;
  text-align: center;
  box-shadow: var(--shadow);
  position: relative;
}
.roadmap-step .step-num {
  width: 32px;
  height: 32px;
  background: var(--primary);
  color: #fff;
  border-radius: 50%;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 0.9rem;
  margin-bottom: 8px;
}
.roadmap-step h4 { font-size: 0.95rem; margin-bottom: 4px; }
.roadmap-step p { font-size: 0.8rem; color: var(--text-light); }

/* ===== 响应式 ===== */
@media (max-width: 768px) {
  .hero h1 { font-size: 1.6rem; }
  .grade-grid { grid-template-columns: 1fr; }
  .container { padding: 20px 16px; }
  .topic-section { padding: 20px; }
  .header-inner { padding: 0 16px; }
  .nav-links { gap: 4px; }
  .nav-links a { padding: 4px 10px; font-size: 0.8rem; }
}

/* ===== 动画 ===== */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}
.topic-section { animation: fadeIn .4s ease; }

/* ===== 打印优化 ===== */
@media print {
  .site-header, .sidebar, .quiz-submit, .site-footer { display: none; }
  .grade-layout { grid-template-columns: 1fr; }
  .topic-section { box-shadow: none; border: 1px solid #ddd; }
}