/* ========================================
   现代风格样式表 - 玻璃拟态设计
   ======================================== */

/* CSS变量定义 */
:root {
    --primary: #6366f1;
    --primary-light: #818cf8;
    --primary-dark: #4f46e5;
    --secondary: #ec4899;
    --accent: #06b6d4;
    --dark: #0f172a;
    --dark-light: #1e293b;
    --gray: #64748b;
    --gray-light: #94a3b8;
    --white: #ffffff;
    --glass-bg: rgba(255, 255, 255, 0.08);
    --glass-border: rgba(255, 255, 255, 0.1);
    --shadow: 0 8px 32px rgba(0, 0, 0, 0.3);
    --shadow-light: 0 4px 16px rgba(0, 0, 0, 0.1);
    --radius: 16px;
    --radius-sm: 8px;
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

/* 基础重置 */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    background: linear-gradient(135deg, #0f172a 0%, #1e1b4b 50%, #312e81 100%);
    min-height: 100vh;
    color: var(--white);
    line-height: 1.6;
    overflow-x: hidden;
}

/* 滚动条美化 */
::-webkit-scrollbar {
    width: 8px;
}

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

::-webkit-scrollbar-thumb {
    background: var(--primary);
    border-radius: 4px;
}

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

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

/* ========================================
   头部导航
   ======================================== */
.header {
    background: var(--glass-bg);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--glass-border);
    position: sticky;
    top: 0;
    z-index: 1000;
    padding: 16px 0;
}

.header .container {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 24px;
}

.logo {
    flex-shrink: 0;
}

.logo img {
    height: 42px;
    width: auto;
    filter: brightness(1.2);
}

/* 导航 */
.nav ul {
    display: flex;
    list-style: none;
    gap: 8px;
}

.nav ul li a {
    display: block;
    padding: 10px 20px;
    color: var(--gray-light);
    text-decoration: none;
    font-size: 15px;
    font-weight: 500;
    border-radius: var(--radius-sm);
    transition: var(--transition);
    position: relative;
}

.nav ul li a:hover,
.nav ul li a.active {
    color: var(--white);
    background: var(--glass-bg);
}

.nav ul li a.active::after {
    content: '';
    position: absolute;
    bottom: 4px;
    left: 20px;
    right: 20px;
    height: 2px;
    background: linear-gradient(90deg, var(--primary), var(--secondary));
    border-radius: 2px;
}

/* 搜索框 */
.search {
    display: flex;
    align-items: center;
    background: var(--glass-bg);
    border: 1px solid var(--glass-border);
    border-radius: 50px;
    padding: 4px;
    transition: var(--transition);
    max-width: 300px;
    flex: 1;
}

.search.focused {
    border-color: var(--primary-light);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.2);
}

.search input {
    flex: 1;
    background: transparent;
    border: none;
    padding: 8px 16px;
    color: var(--white);
    font-size: 14px;
    outline: none;
}

.search input::placeholder {
    color: var(--gray);
}

.search button {
    background: linear-gradient(135deg, var(--primary), var(--primary-dark));
    border: none;
    width: 36px;
    height: 36px;
    border-radius: 50%;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--white);
    transition: var(--transition);
}

.search button:hover {
    transform: scale(1.1);
    box-shadow: 0 4px 12px rgba(99, 102, 241, 0.4);
}

/* 用户 */
.user {
    display: flex;
    align-items: center;
    gap: 8px;
    color: var(--gray-light);
    font-size: 14px;
}

.user img {
    width: 36px;
    height: 36px;
    border-radius: 50%;
    border: 2px solid var(--glass-border);
}

/* ========================================
   Hero区域（首页）
   ======================================== */
.hero {
    padding: 80px 0;
    text-align: center;
    position: relative;
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 600px;
    height: 600px;
    background: radial-gradient(circle, rgba(99, 102, 241, 0.3) 0%, transparent 70%);
    pointer-events: none;
}

.hero-content {
    position: relative;
    z-index: 1;
}

.hero-title {
    font-size: 48px;
    font-weight: 700;
    background: linear-gradient(135deg, var(--white) 0%, var(--primary-light) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 16px;
    letter-spacing: -1px;
}

.hero-subtitle {
    font-size: 20px;
    color: var(--gray-light);
    font-weight: 300;
}

.hero-decoration {
    width: 60px;
    height: 4px;
    background: linear-gradient(90deg, var(--primary), var(--secondary));
    border-radius: 2px;
    margin: 24px auto 0;
}

/* ========================================
   章节卡片（首页）
   ======================================== */
.chapters {
    padding: 40px 0 80px;
}

.section-title {
    font-size: 28px;
    font-weight: 600;
    text-align: center;
    margin-bottom: 48px;
    background: linear-gradient(135deg, var(--white) 0%, var(--primary-light) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.chapters-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 20px;
}

.chapter-card {
    display: flex;
    align-items: center;
    gap: 16px;
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius);
    padding: 24px;
    text-decoration: none;
    color: var(--white);
    transition: var(--transition);
    opacity: 0;
    transform: translateY(20px);
}

.chapter-card.visible {
    opacity: 1;
    transform: translateY(0);
}

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

.chapter-number {
    width: 48px;
    height: 48px;
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 18px;
    font-weight: 700;
    flex-shrink: 0;
}

.chapter-info {
    flex: 1;
}

.chapter-info h3 {
    font-size: 16px;
    font-weight: 600;
    margin-bottom: 4px;
}

.chapter-info p {
    font-size: 13px;
    color: var(--gray-light);
}

.chapter-arrow {
    color: var(--gray);
    transition: var(--transition);
}

.chapter-card:hover .chapter-arrow {
    color: var(--primary-light);
    transform: translateX(4px);
}

/* ========================================
   页面头部（list页）
   ======================================== */
.page-header {
    padding: 60px 0 40px;
    text-align: center;
}

.page-header h1 {
    font-size: 36px;
    font-weight: 700;
    background: linear-gradient(135deg, var(--white) 0%, var(--primary-light) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 16px;
}

.breadcrumb {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    color: var(--gray-light);
    font-size: 14px;
}

.breadcrumb a {
    color: var(--primary-light);
    text-decoration: none;
    transition: var(--transition);
}

.breadcrumb a:hover {
    color: var(--white);
}

.breadcrumb .separator {
    display: flex;
    align-items: center;
    opacity: 0.5;
}

.breadcrumb .current {
    color: var(--gray);
}

/* ========================================
   课程预览（list页）
   ======================================== */
.course-preview {
    padding: 0 0 40px;
}

.preview-card {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 40px;
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius);
    padding: 32px;
    overflow: hidden;
}

.preview-image {
    border-radius: var(--radius-sm);
    overflow: hidden;
}

.preview-image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: var(--transition);
}

.preview-card:hover .preview-image img {
    transform: scale(1.05);
}

.preview-info {
    display: flex;
    flex-direction: column;
    justify-content: center;
}

.preview-info h2 {
    font-size: 24px;
    font-weight: 600;
    margin-bottom: 16px;
    background: linear-gradient(135deg, var(--white) 0%, var(--primary-light) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.preview-info p {
    color: var(--gray-light);
    line-height: 1.8;
    margin-bottom: 24px;
}

.preview-stats {
    display: flex;
    gap: 32px;
}

.stat {
    text-align: center;
}

.stat-number {
    display: block;
    font-size: 28px;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary), var(--accent));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.stat-label {
    font-size: 13px;
    color: var(--gray);
}

/* ========================================
   章节列表（list页）
   ======================================== */
.chapters-list {
    padding: 40px 0 80px;
}

.list-grid {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.list-item {
    display: flex;
    align-items: center;
    gap: 20px;
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-sm);
    padding: 20px 24px;
    text-decoration: none;
    color: var(--white);
    transition: var(--transition);
    opacity: 0;
    transform: translateX(-20px);
}

.list-item.visible {
    opacity: 1;
    transform: translateX(0);
}

.list-item:hover {
    border-color: var(--primary-light);
    transform: translateX(8px);
    box-shadow: var(--shadow-light);
}

.item-number {
    width: 40px;
    height: 40px;
    background: linear-gradient(135deg, var(--primary), var(--primary-dark));
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 14px;
    font-weight: 700;
    flex-shrink: 0;
}

.item-content {
    flex: 1;
}

.item-content h3 {
    font-size: 16px;
    font-weight: 600;
    margin-bottom: 4px;
}

.item-content p {
    font-size: 13px;
    color: var(--gray-light);
}

.item-arrow {
    color: var(--gray);
    transition: var(--transition);
}

.list-item:hover .item-arrow {
    color: var(--primary-light);
    transform: translateX(4px);
}

/* ========================================
   页脚
   ======================================== */
.footer {
    background: var(--glass-bg);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-top: 1px solid var(--glass-border);
    padding: 40px 0;
    margin-top: auto;
}

.footer-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 20px;
}

.footer-brand {
    display: flex;
    align-items: center;
    gap: 12px;
}

.footer-logo {
    height: 36px;
    width: auto;
    filter: brightness(1.2);
}

.footer-brand p {
    color: var(--gray-light);
    font-size: 14px;
}

.footer-info {
    text-align: right;
}

.footer-info p {
    color: var(--gray);
    font-size: 13px;
    margin-bottom: 4px;
}

.footer-info .copyright {
    color: var(--gray-light);
    font-size: 12px;
}

/* ========================================
   响应式设计
   ======================================== */
@media (max-width: 768px) {
    .header .container {
        flex-wrap: wrap;
    }

    .nav {
        order: 3;
        width: 100%;
    }

    .nav ul {
        justify-content: center;
    }

    .search {
        max-width: 200px;
    }

    .hero-title {
        font-size: 32px;
    }

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

    .preview-card {
        grid-template-columns: 1fr;
    }

    .preview-stats {
        justify-content: center;
    }

    .footer-content {
        flex-direction: column;
        text-align: center;
    }

    .footer-info {
        text-align: center;
    }
}

/* ========================================
   动画
   ======================================== */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes pulse {
    0%, 100% {
        opacity: 1;
    }
    50% {
        opacity: 0.7;
    }
}