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

body {
    font-family: 'Segoe UI', 'PingFang SC', 'Microsoft YaHei', sans-serif;
    line-height: 1.8;
    color: #2d3748;
    background: linear-gradient(135deg, #f0fff4 0%, #e6fffa 50%, #ebf8ff 100%);
}

/* ===== 导航栏 ===== */
.top-nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: 60px;
    background: linear-gradient(135deg, #38a169 0%, #48bb78 100%);
    display: flex;
    align-items: center;
    padding: 0 24px;
    z-index: 1000;
    box-shadow: 0 2px 15px rgba(56, 161, 105, 0.3);
}

.nav-back {
    color: white;
    text-decoration: none;
    font-weight: bold;
    font-size: 0.95rem;
    padding: 8px 16px;
    border-radius: 20px;
    background: rgba(255, 255, 255, 0.2);
    transition: all 0.3s ease;
}

.nav-back:hover {
    background: rgba(255, 255, 255, 0.35);
}

.nav-title {
    flex: 1;
    text-align: center;
    color: white;
    font-size: 1.3rem;
}

/* ===== 主内容 ===== */
.content {
    margin-top: 60px;
    padding: 40px 20px;
    max-width: 900px;
    margin-left: auto;
    margin-right: auto;
}

/* ===== 课程介绍 ===== */
.course-intro-section {
    text-align: center;
    padding: 40px 20px;
    background: white;
    border-radius: 20px;
    margin-bottom: 30px;
    box-shadow: 0 4px 20px rgba(56, 161, 105, 0.1);
    border: 2px solid rgba(72, 187, 120, 0.15);
}

.course-intro-section h2 {
    font-size: 2rem;
    color: #276749;
    margin-bottom: 15px;
}

.course-intro-section p {
    font-size: 1.1rem;
    color: #4a5568;
}

/* ===== 课程章节 ===== */
.chapters-section {
    background: white;
    border-radius: 20px;
    padding: 30px;
    margin-bottom: 30px;
    box-shadow: 0 4px 20px rgba(56, 161, 105, 0.1);
    border: 2px solid rgba(72, 187, 120, 0.15);
}

.chapters-section h3 {
    font-size: 1.3rem;
    color: #276749;
    margin-bottom: 20px;
}

.chapters-list {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 12px;
}

.chapter-btn {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 14px 18px;
    background: #f7fafc;
    border: 2px solid #e2e8f0;
    border-radius: 12px;
    font-size: 0.95rem;
    color: #4a5568;
    cursor: pointer;
    transition: all 0.3s ease;
    text-align: left;
}

.chapter-btn:hover {
    border-color: #48bb78;
    background: #f0fff4;
}

.chapter-btn.active {
    background: linear-gradient(135deg, #48bb78, #38a169);
    color: white;
    border-color: transparent;
}

.chapter-btn .time {
    font-size: 0.8rem;
    opacity: 0.7;
}

/* ===== 章节内容 ===== */
.chapter-content {
    background: white;
    border-radius: 20px;
    padding: 40px;
    box-shadow: 0 4px 20px rgba(56, 161, 105, 0.1);
    border: 2px solid rgba(72, 187, 120, 0.15);
}

.chapter-content h1 {
    font-size: 2rem;
    color: #276749;
    margin-bottom: 25px;
    padding-bottom: 15px;
    border-bottom: 3px solid #48bb78;
}

.chapter-content h2 {
    font-size: 1.5rem;
    color: #2d3748;
    margin: 30px 0 15px;
}

.chapter-content h3 {
    font-size: 1.2rem;
    color: #4a5568;
    margin: 20px 0 10px;
}

.chapter-content p {
    color: #4a5568;
    margin-bottom: 15px;
}

.chapter-content ul, .chapter-content ol {
    margin: 15px 0 15px 25px;
    color: #4a5568;
}

.chapter-content li {
    margin-bottom: 8px;
}

/* ===== 导学框 ===== */
.guide-box {
    background: linear-gradient(135deg, #f0fff4, #e6fffa);
    border-left: 4px solid #48bb78;
    padding: 20px;
    border-radius: 0 12px 12px 0;
    margin-bottom: 25px;
}

.guide-box h3 {
    margin-top: 0;
    color: #276749;
}

.guide-box p {
    margin-bottom: 0;
}

/* ===== 表格 ===== */
.feature-table, .summary-table {
    width: 100%;
    border-collapse: collapse;
    margin: 20px 0;
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.05);
}

.feature-table th, .summary-table th {
    background: linear-gradient(135deg, #48bb78, #38a169);
    color: white;
    padding: 14px 18px;
    text-align: left;
}

.feature-table td, .summary-table td {
    padding: 14px 18px;
    border-bottom: 1px solid #e2e8f0;
    background: white;
}

.feature-table tr:last-child td, .summary-table tr:last-child td {
    border-bottom: none;
}

.feature-table tr:hover td, .summary-table tr:hover td {
    background: #f7fafc;
}

/* ===== 代码块 ===== */
.code-block {
    background: #1e1e2e;
    border-radius: 12px;
    overflow: hidden;
    margin: 15px 0;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
}

.code-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 10px 16px;
    background: #2d2d3d;
    color: #a0aec0;
    font-size: 0.85rem;
}

.copy-btn {
    background: transparent;
    border: 1px solid #4a5568;
    color: #a0aec0;
    padding: 4px 12px;
    border-radius: 6px;
    cursor: pointer;
    font-size: 0.8rem;
    transition: all 0.2s;
}

.copy-btn:hover {
    border-color: #48bb78;
    color: #48bb78;
}

.code-block pre {
    padding: 20px;
    overflow-x: auto;
}

.code-block code {
    font-family: 'Consolas', 'Monaco', 'Courier New', monospace;
    font-size: 0.9rem;
    color: #e2e8f0;
    line-height: 1.6;
}

/* ===== 链接卡片 ===== */
.links-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 15px;
    margin: 20px 0;
}

.link-card {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 20px;
    background: #f7fafc;
    border: 2px solid #e2e8f0;
    border-radius: 12px;
    text-decoration: none;
    transition: all 0.3s ease;
}

.link-card:hover {
    border-color: #48bb78;
    transform: translateY(-3px);
    box-shadow: 0 6px 20px rgba(72, 187, 120, 0.15);
}

.link-icon {
    font-size: 2rem;
    margin-bottom: 8px;
}

.link-card span {
    font-weight: 600;
    color: #2d3748;
}

.link-card small {
    color: #718096;
    font-size: 0.8rem;
    margin-top: 4px;
}

/* ===== 用途网格 ===== */
.usage-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 20px;
    margin: 20px 0;
}

.usage-item {
    text-align: center;
    padding: 25px 15px;
    background: linear-gradient(135deg, #f0fff4, #e6fffa);
    border-radius: 16px;
    border: 1px solid rgba(72, 187, 120, 0.2);
}

.usage-icon {
    font-size: 2.5rem;
    display: block;
    margin-bottom: 10px;
}

.usage-item h4 {
    color: #276749;
    margin-bottom: 5px;
}

.usage-item p {
    color: #718096;
    font-size: 0.9rem;
    margin: 0;
}

/* ===== 练习框 ===== */
.practice-box {
    background: linear-gradient(135deg, #faf5ff, #fef3c7);
    border: 2px solid #d69e2e;
    border-radius: 16px;
    padding: 25px;
    margin: 30px 0;
}

.practice-box h3 {
    color: #975a16;
    margin-bottom: 15px;
}

.practice-box ol {
    margin-left: 20px;
}

.practice-box li {
    margin-bottom: 10px;
    color: #4a5568;
}

/* ===== 章节导航 ===== */
.chapter-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 40px;
    padding-top: 20px;
    border-top: 2px solid #e2e8f0;
}

.next-btn {
    background: linear-gradient(135deg, #48bb78, #38a169);
    color: white;
    border: none;
    padding: 12px 28px;
    border-radius: 30px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
}

.next-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(72, 187, 120, 0.3);
}

/* ===== 回到顶部 ===== */
.back-to-top {
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 48px;
    height: 48px;
    background: linear-gradient(135deg, #48bb78, #38a169);
    color: white;
    border: none;
    border-radius: 50%;
    font-size: 1.3rem;
    cursor: pointer;
    box-shadow: 0 4px 15px rgba(72, 187, 120, 0.3);
    opacity: 0;
    transform: translateY(20px);
    transition: all 0.3s ease;
    z-index: 800;
}

.back-to-top.visible {
    opacity: 1;
    transform: translateY(0);
}

.back-to-top:hover {
    transform: translateY(-3px);
    box-shadow: 0 6px 20px rgba(72, 187, 120, 0.5);
}

/* ===== 响应式 ===== */
@media (max-width: 768px) {
    .content {
        padding: 20px 15px;
    }

    .chapter-content {
        padding: 25px;
    }

    .course-intro-section h2, .chapter-content h1 {
        font-size: 1.6rem;
    }

    .chapters-list {
        grid-template-columns: 1fr;
    }
}