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

:root {
    --primary-color: #4f46e5;
    --primary-hover: #4338ca;
    --secondary-color: #6366f1;
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --border-color: #e2e8f0;
    --success-color: #10b981;
    --warning-color: #f59e0b;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
    --radius: 12px;
    --radius-lg: 20px;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* 页面切换 */
.page {
    display: none;
    min-height: 100vh;
}

.page.active {
    display: flex;
    flex-direction: column;
}

/* ==================== 首页封面 ==================== */
.hero {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    position: relative;
    padding: 40px 20px;
    overflow: hidden;
}

.hero-bg {
    position: absolute;
    inset: 0;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 50%, #f093fb 100%);
    opacity: 0.95;
}

.hero-bg::before {
    content: '';
    position: absolute;
    inset: 0;
    background: url("data:image/svg+xml,%3Csvg width='60' height='60' viewBox='0 0 60 60' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='none' fill-rule='evenodd'%3E%3Cg fill='%23ffffff' fill-opacity='0.05'%3E%3Cpath d='M36 34v-4h-2v4h-4v2h4v4h2v-4h4v-2h-4zm0-30V0h-2v4h-4v2h4v4h2V6h4V4h-4zM6 34v-4H4v4H0v2h4v4h2v-4h4v-2H6zM6 4V0H4v4H0v2h4v4h2V6h4V4H6z'/%3E%3C/g%3E%3C/g%3E%3C/svg%3E");
}

.hero-content {
    position: relative;
    z-index: 1;
    text-align: center;
    color: white;
    max-width: 900px;
}

.hero-icon {
    width: 100px;
    height: 100px;
    background: rgba(255, 255, 255, 0.2);
    backdrop-filter: blur(10px);
    border-radius: 30px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 0 auto 24px;
    font-size: 3rem;
}

.hero-title {
    font-size: 3rem;
    font-weight: 800;
    margin-bottom: 12px;
    text-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
}

.hero-subtitle {
    font-size: 1.3rem;
    opacity: 0.9;
    margin-bottom: 50px;
}

/* 年级卡片 */
.grade-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
    gap: 20px;
    max-width: 900px;
    margin: 0 auto;
}

.grade-card {
    background: rgba(255, 255, 255, 0.95);
    border-radius: var(--radius-lg);
    padding: 30px 20px;
    cursor: pointer;
    transition: all 0.3s ease;
    color: var(--text-primary);
    box-shadow: var(--shadow-lg);
}

.grade-card:hover {
    transform: translateY(-8px);
    box-shadow: var(--shadow-xl);
}

.grade-card .grade-icon {
    width: 60px;
    height: 60px;
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--secondary-color) 100%);
    border-radius: 16px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 0 auto 16px;
    font-size: 1.8rem;
    color: white;
}

.grade-card .grade-icon.gaokao {
    background: linear-gradient(135deg, #ef4444 0%, #f97316 100%);
}

.grade-card .grade-icon.competition {
    background: linear-gradient(135deg, #f59e0b 0%, #fbbf24 100%);
}

.grade-card h3 {
    font-size: 1.3rem;
    font-weight: 700;
    margin-bottom: 6px;
}

.grade-card p {
    font-size: 0.9rem;
    color: var(--text-secondary);
}

/* ==================== 年级详情页 ==================== */
.page-header {
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--secondary-color) 100%);
    color: white;
    padding: 20px;
    display: flex;
    align-items: center;
    gap: 20px;
}

.back-btn {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 10px 20px;
    background: rgba(255, 255, 255, 0.2);
    border: none;
    border-radius: var(--radius);
    color: white;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.2s ease;
}

.back-btn:hover {
    background: rgba(255, 255, 255, 0.3);
}

.page-header h1 {
    font-size: 1.5rem;
    font-weight: 600;
}

.grade-content {
    flex: 1;
    padding: 30px 0;
}

/* 文件夹网格 */
.folder-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 24px;
    margin-bottom: 30px;
}

.folder-card {
    background: var(--card-bg);
    border-radius: var(--radius-lg);
    padding: 30px;
    cursor: pointer;
    transition: all 0.3s ease;
    border: 2px solid var(--border-color);
    text-align: center;
}

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

.folder-icon {
    width: 70px;
    height: 70px;
    border-radius: 20px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 0 auto 20px;
    font-size: 2rem;
    color: white;
}

.folder-icon.exams {
    background: linear-gradient(135deg, #3b82f6 0%, #60a5fa 100%);
}

.folder-icon.chapters {
    background: linear-gradient(135deg, #10b981 0%, #34d399 100%);
}

.folder-icon.mock {
    background: linear-gradient(135deg, #f59e0b 0%, #fbbf24 100%);
}

.folder-card h3 {
    font-size: 1.3rem;
    font-weight: 600;
    margin-bottom: 8px;
    color: var(--text-primary);
}

.folder-count {
    font-size: 0.95rem;
    color: var(--text-secondary);
}

/* 文件列表区域 */
.file-section {
    animation: fadeIn 0.3s ease;
}

.section-header {
    display: flex;
    align-items: center;
    gap: 16px;
    margin-bottom: 20px;
    flex-wrap: wrap;
}

.back-folder-btn {
    display: flex;
    align-items: center;
    gap: 6px;
    padding: 8px 16px;
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    color: var(--text-secondary);
    font-size: 0.9rem;
    cursor: pointer;
    transition: all 0.2s ease;
}

.back-folder-btn:hover {
    background: var(--border-color);
    color: var(--text-primary);
}

.section-header h2 {
    font-size: 1.4rem;
    font-weight: 600;
    flex: 1;
}

.file-count {
    background: var(--primary-color);
    color: white;
    padding: 6px 14px;
    border-radius: 20px;
    font-size: 0.9rem;
}

/* 搜索栏 */
.search-bar {
    position: relative;
    margin-bottom: 24px;
}

.search-bar i {
    position: absolute;
    left: 16px;
    top: 50%;
    transform: translateY(-50%);
    color: var(--text-secondary);
}

.search-bar input {
    width: 100%;
    padding: 14px 16px 14px 48px;
    border: 2px solid var(--border-color);
    border-radius: var(--radius);
    font-size: 1rem;
    transition: all 0.2s ease;
    background: var(--card-bg);
}

.search-bar input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
}

/* 文件网格 */
.file-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 20px;
}

/* 文件卡片 */
.file-card {
    background: var(--card-bg);
    border-radius: var(--radius);
    padding: 20px;
    border: 1px solid var(--border-color);
    transition: all 0.2s ease;
    display: flex;
    flex-direction: column;
}

.file-card:hover {
    box-shadow: var(--shadow-lg);
    transform: translateY(-2px);
    border-color: var(--primary-color);
}

.file-icon {
    width: 48px;
    height: 48px;
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--secondary-color) 100%);
    border-radius: 12px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 16px;
    font-size: 1.4rem;
    color: white;
}

.file-name {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
    line-height: 1.4;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.file-info {
    display: flex;
    gap: 16px;
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-bottom: 16px;
}

.file-info span {
    display: flex;
    align-items: center;
    gap: 4px;
}

/* 下载按钮组 */
.download-buttons {
    display: flex;
    gap: 10px;
    margin-top: auto;
}

.download-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 6px;
    padding: 10px 16px;
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 0.9rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s ease;
    text-decoration: none;
    flex: 1;
}

.download-btn i {
    font-size: 0.95rem;
}

.paper-btn {
    background: var(--primary-color);
}

.paper-btn:hover {
    background: var(--primary-hover);
}

.answer-btn {
    background: var(--success-color);
}

.answer-btn:hover {
    background: #059669;
}

/* 空状态 */
.empty-state {
    text-align: center;
    padding: 60px 20px;
    color: var(--text-secondary);
}

.empty-state i {
    font-size: 4rem;
    margin-bottom: 16px;
    opacity: 0.5;
}

.empty-state p {
    font-size: 1.2rem;
    font-weight: 500;
    margin-bottom: 8px;
    color: var(--text-primary);
}

/* 页脚 */
.footer {
    background: rgba(0, 0, 0, 0.1);
    padding: 20px;
    text-align: center;
    color: rgba(255, 255, 255, 0.8);
    font-size: 0.9rem;
}

/* 响应式 */
@media (max-width: 768px) {
    .hero-title {
        font-size: 2rem;
    }

    .hero-subtitle {
        font-size: 1.1rem;
    }

    .grade-cards {
        grid-template-columns: repeat(2, 1fr);
        gap: 12px;
    }

    .grade-card {
        padding: 20px 15px;
    }

    .grade-card .grade-icon {
        width: 50px;
        height: 50px;
        font-size: 1.5rem;
    }

    .grade-card h3 {
        font-size: 1.1rem;
    }

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

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

    .page-header {
        flex-direction: column;
        align-items: flex-start;
        gap: 12px;
    }

    .section-header {
        flex-direction: column;
        align-items: flex-start;
    }
}

/* 动画 */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.file-card {
    animation: fadeIn 0.3s ease forwards;
}

.file-card:nth-child(1) { animation-delay: 0.05s; }
.file-card:nth-child(2) { animation-delay: 0.1s; }
.file-card:nth-child(3) { animation-delay: 0.15s; }
.file-card:nth-child(4) { animation-delay: 0.2s; }
.file-card:nth-child(5) { animation-delay: 0.25s; }
.file-card:nth-child(6) { animation-delay: 0.3s; }