:root {
  --primary-color: #2563eb;
  --primary-hover: #1d4ed8;
  --bg-color: #f3f4f6;
  --card-bg: #ffffff;
  --text-main: #1f2937;
  --text-muted: #6b7280;
  --border-color: #e5e7eb;
  --nav-bg: #ffffff;
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background-color: var(--bg-color);
  color: var(--text-main);
  line-height: 1.6;
}

/* 导航栏 */
.header {
  position: sticky;
  top: 0;
  background-color: var(--nav-bg);
  box-shadow: var(--shadow-sm);
  z-index: 100;
}

.nav-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 1rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
}

.logo {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary-color);
  text-decoration: none;
}

.nav-links {
  display: flex;
  gap: 1.5rem;
}

.nav-item {
  color: var(--text-muted);
  text-decoration: none;
  font-weight: 500;
  padding: 0.5rem 0;
  border-bottom: 2px solid transparent;
  transition: all 0.2s;
  cursor: pointer;
}

.nav-item:hover {
  color: var(--primary-color);
}

.nav-item.active {
  color: var(--primary-color);
  border-bottom-color: var(--primary-color);
}

.search-box {
  flex-grow: 1;
  max-width: 300px;
  position: relative;
}

.search-box input {
  width: 100%;
  padding: 0.5rem 1rem;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  outline: none;
  font-size: 0.95rem;
  transition: border-color 0.2s;
}

.search-box input:focus {
  border-color: var(--primary-color);
}

/* 主体内区域 */
.main-content {
  max-width: 1200px;
  margin: 2rem auto;
  padding: 0 1rem;
  min-height: calc(100vh - 160px);
}

.welcome-section {
  text-align: center;
  margin-bottom: 3rem;
  padding: 3rem 1rem;
  background-color: var(--card-bg);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
}

.welcome-section h1 {
  font-size: 2rem;
  margin-bottom: 1rem;
  color: var(--text-main);
}

.welcome-section p {
  color: var(--text-muted);
  font-size: 1.1rem;
  max-width: 600px;
  margin: 0 auto;
}

.section-title {
  margin-bottom: 1.5rem;
  font-size: 1.5rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

/* 卡片网格 */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 1.5rem;
  margin-bottom: 3rem;
}

.card {
  background-color: var(--card-bg);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
  transition: transform 0.2s, box-shadow 0.2s;
  display: flex;
  flex-direction: column;
}

.card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.card-module-badge {
  font-size: 0.75rem;
  background-color: #e0f2fe;
  color: #0284c7;
  padding: 0.2rem 0.6rem;
  border-radius: 1rem;
  align-self: flex-start;
  margin-bottom: 0.75rem;
  font-weight: 500;
}

.card-title {
  font-size: 1.1rem;
  font-weight: 600;
  margin-bottom: 0.75rem;
  color: var(--text-main);
}

.card-content {
  color: var(--text-muted);
  font-size: 0.95rem;
  flex-grow: 1;
  margin-bottom: 1rem;
  /* 限制行数 */
  display: -webkit-box;
  -webkit-line-clamp: 4;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.card-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: auto;
}

.tag {
  font-size: 0.75rem;
  background-color: var(--bg-color);
  color: var(--text-muted);
  padding: 0.2rem 0.5rem;
  border-radius: 0.25rem;
}

/* 模块首页入口卡片 */
.module-entry {
  text-align: center;
  justify-content: center;
  align-items: center;
  cursor: pointer;
  background: linear-gradient(145deg, #ffffff, #f9fafb);
  border: 1px solid var(--border-color);
  min-height: 180px;
}

.module-entry:hover {
  border-color: var(--primary-color);
}

.module-entry h3 {
  font-size: 1.5rem;
  color: var(--primary-color);
  margin-bottom: 0.5rem;
}

/* 状态提示 */
.empty-state {
  text-align: center;
  padding: 4rem 2rem;
  color: var(--text-muted);
  background-color: var(--card-bg);
  border-radius: var(--radius-lg);
  grid-column: 1 / -1;
}

/* 页脚 */
.footer {
  text-align: center;
  padding: 2rem;
  color: var(--text-muted);
  font-size: 0.9rem;
  border-top: 1px solid var(--border-color);
}

/* 响应式 */
@media (max-width: 640px) {
  .nav-container {
    flex-direction: column;
    align-items: flex-start;
  }
  
  .search-box {
    max-width: 100%;
    width: 100%;
    order: 3;
  }
  
  .nav-links {
    width: 100%;
    justify-content: space-between;
    order: 2;
  }
}