/* ===== 基础样式 ===== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary-color: #667eea;
    --primary-dark: #5a67d8;
    --secondary-color: #764ba2;
    --success-color: #48bb78;
    --danger-color: #f56565;
    --warning-color: #ed8936;
    --info-color: #4299e1;
    --text-primary: #1a202c;
    --text-secondary: #4a5568;
    --text-light: #718096;
    --bg-primary: #ffffff;
    --bg-secondary: #f7fafc;
    --border-color: #e2e8f0;
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.15);
    --shadow-xl: 0 20px 40px rgba(0, 0, 0, 0.2);
    --transition: all 0.3s ease;
}

body {
    font-family: 'Noto Serif SC', serif;
    background: linear-gradient(135deg, #1e3c72 0%, #2a5298 50%, #7e8ba3 100%);
    background-attachment: fixed;
    min-height: 100vh;
    color: var(--text-primary);
}

/* ===== 导航栏样式 ===== */
.navbar {
    background: rgba(255, 255, 255, 0.98);
    backdrop-filter: blur(20px);
    box-shadow: var(--shadow-md);
    position: fixed;
    width: 100%;
    top: 0;
    z-index: 1000;
    transition: var(--transition);
}

.navbar.scrolled {
    padding: 8px 0;
}

.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px 40px;
    max-width: 1400px;
    margin: 0 auto;
}

.logo {
    font-size: 26px;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: 2px;
    flex-shrink: 0;
}

.nav-center {
    flex: 1;
    display: flex;
    justify-content: center;
    padding: 0 40px;
}

.nav-right {
    display: flex;
    align-items: center;
    gap: 30px;
}

/* 搜索框 */
.search-container {
    position: relative;
    max-width: 400px;
    width: 100%;
}

.search-input {
    width: 100%;
    padding: 12px 50px 12px 20px;
    border: 2px solid var(--border-color);
    border-radius: 25px;
    font-size: 14px;
    transition: var(--transition);
    background: var(--bg-secondary);
}

.search-input:focus {
    outline: none;
    border-color: var(--primary-color);
    background: var(--bg-primary);
    box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.1);
}

.search-btn {
    position: absolute;
    right: 8px;
    top: 50%;
    transform: translateY(-50%);
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    border: none;
    border-radius: 50%;
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: var(--transition);
    color: white;
}

.search-btn:hover {
    transform: translateY(-50%) scale(1.05);
}

.search-dropdown {
    position: absolute;
    top: calc(100% + 8px);
    left: 0;
    right: 0;
    background: white;
    border-radius: 12px;
    box-shadow: var(--shadow-lg);
    max-height: 400px;
    overflow-y: auto;
    display: none;
}

.search-dropdown.active {
    display: block;
}

.search-dropdown-item {
    padding: 12px 16px;
    border-bottom: 1px solid var(--border-color);
    cursor: pointer;
    transition: var(--transition);
}

.search-dropdown-item:hover {
    background: var(--bg-secondary);
}

.search-dropdown-item:last-child {
    border-bottom: none;
}

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

.nav-item {
    cursor: pointer;
    padding: 10px 20px;
    border-radius: 20px;
    transition: var(--transition);
    font-weight: 500;
    position: relative;
    overflow: hidden;
}

.nav-item::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    transition: left 0.3s ease;
    z-index: -1;
    border-radius: 20px;
}

.nav-item:hover::before,
.nav-item.active::before {
    left: 0;
}

.nav-item:hover,
.nav-item.active {
    color: white;
}

/* 用户菜单 */
.user-menu {
    position: relative;
}

.user-btn {
    background: transparent;
    border: none;
    cursor: pointer;
    padding: 8px;
    border-radius: 50%;
    transition: var(--transition);
    color: var(--text-secondary);
}

.user-btn:hover {
    background: var(--bg-secondary);
    color: var(--primary-color);
}

.user-dropdown {
    position: absolute;
    top: calc(100% + 8px);
    right: 0;
    background: white;
    border-radius: 12px;
    box-shadow: var(--shadow-lg);
    min-width: 200px;
    overflow: hidden;
    display: none;
    z-index: 1001;
}

.user-dropdown.active {
    display: block;
    animation: fadeInDown 0.2s ease;
}

@keyframes fadeInDown {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.user-info {
    padding: 16px;
    border-bottom: 1px solid var(--border-color);
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
}

.user-name {
    display: block;
    font-weight: 600;
    font-size: 16px;
}

.user-role {
    display: block;
    font-size: 12px;
    opacity: 0.8;
    margin-top: 4px;
}

.user-dropdown-item {
    display: block;
    padding: 12px 16px;
    color: var(--text-primary);
    text-decoration: none;
    transition: var(--transition);
}

.user-dropdown-item:hover {
    background: var(--bg-secondary);
}

/* ===== 主内容区域 ===== */
.main-content {
    margin-top: 80px;
    padding: 40px;
    max-width: 1400px;
    margin-left: auto;
    margin-right: auto;
}

.module {
    display: none;
    animation: fadeInUp 0.5s ease-out;
}

.module.active {
    display: block;
}

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

/* ===== 数学文化模块 ===== */
.culture-header {
    text-align: center;
    margin-bottom: 40px;
}

.culture-title-main,
.problems-title-main,
.videos-title-main {
    font-size: 42px;
    color: white;
    margin-bottom: 15px;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.3);
}

.culture-subtitle,
.problems-subtitle,
.videos-subtitle {
    font-size: 18px;
    color: rgba(255, 255, 255, 0.85);
    font-style: italic;
}

.culture-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
    gap: 30px;
}

.culture-card {
    background: rgba(255, 255, 255, 0.98);
    border-radius: 20px;
    overflow: hidden;
    box-shadow: var(--shadow-lg);
    transition: var(--transition);
    cursor: pointer;
}

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

.culture-image {
    width: 100%;
    height: 200px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-size: 64px;
    font-weight: 700;
    position: relative;
    overflow: hidden;
}

.culture-image::after {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(45deg, transparent 30%, rgba(255, 255, 255, 0.1) 50%, transparent 70%);
    transition: transform 0.6s;
}

.culture-card:hover .culture-image::after {
    transform: translateX(200%);
}

.culture-content {
    padding: 25px;
}

.culture-title {
    font-size: 20px;
    font-weight: 700;
    margin-bottom: 12px;
    color: var(--text-primary);
    line-height: 1.4;
}

.culture-desc {
    color: var(--text-secondary);
    line-height: 1.7;
    font-size: 15px;
    display: -webkit-box;
    -webkit-line-clamp: 4;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.culture-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 15px;
    padding-top: 15px;
    border-top: 1px solid var(--border-color);
}

.culture-actions {
    display: flex;
    gap: 8px;
}

.icon-btn {
    background: transparent;
    border: none;
    cursor: pointer;
    padding: 6px 10px;
    border-radius: 8px;
    transition: var(--transition);
    color: var(--text-light);
    font-size: 14px;
}

.icon-btn:hover {
    background: var(--bg-secondary);
    color: var(--primary-color);
}

/* ===== 习题库模块 ===== */
.filters {
    display: flex;
    gap: 15px;
    justify-content: center;
    margin-top: 20px;
    flex-wrap: wrap;
}

.filter-select {
    padding: 10px 20px;
    border: 2px solid rgba(255, 255, 255, 0.3);
    border-radius: 25px;
    background: rgba(255, 255, 255, 0.9);
    color: var(--text-primary);
    font-size: 14px;
    cursor: pointer;
    transition: var(--transition);
}

.filter-select:focus {
    outline: none;
    border-color: var(--primary-color);
    background: white;
}

.problems-list {
    display: flex;
    flex-direction: column;
    gap: 20px;
    margin-top: 30px;
}

.problem-container {
    background: rgba(255, 255, 255, 0.98);
    border-radius: 16px;
    padding: 30px;
    box-shadow: var(--shadow-lg);
    transition: var(--transition);
    border-left: 4px solid var(--primary-color);
}

.problem-container:hover {
    transform: translateX(5px);
    box-shadow: var(--shadow-xl);
}

.problem-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: 20px;
    gap: 15px;
    flex-wrap: wrap;
}

.problem-title {
    font-size: 20px;
    font-weight: 700;
    color: var(--text-primary);
    line-height: 1.5;
    flex: 1;
    min-width: 200px;
}

.problem-level {
    padding: 6px 16px;
    border-radius: 20px;
    font-size: 13px;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    flex-shrink: 0;
}

.level-easy {
    background: #d1fae5;
    color: #065f46;
}

.level-medium {
    background: #fef3c7;
    color: #92400e;
}

.level-hard {
    background: #fee2e2;
    color: #991b1b;
}

.level-advanced {
    background: #dbeafe;
    color: #1e40af;
}

.problem-content {
    color: var(--text-secondary);
    line-height: 1.7;
    font-size: 15px;
}

.problem-tags {
    margin-top: 15px;
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

.tag {
    background: var(--bg-secondary);
    padding: 4px 12px;
    border-radius: 12px;
    font-size: 13px;
    color: var(--text-secondary);
}

.problem-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 15px;
    padding-top: 15px;
    border-top: 1px solid var(--border-color);
}

.problem-stats {
    display: flex;
    gap: 15px;
    color: var(--text-light);
    font-size: 14px;
}

/* ===== 视频模块 ===== */
.video-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
    gap: 30px;
    margin-top: 30px;
}

.video-card {
    background: rgba(255, 255, 255, 0.98);
    border-radius: 16px;
    overflow: hidden;
    box-shadow: var(--shadow-lg);
    transition: var(--transition);
}

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

.video-thumbnail {
    width: 100%;
    height: 200px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-size: 64px;
    cursor: pointer;
    position: relative;
    transition: var(--transition);
}

.video-thumbnail:hover {
    transform: scale(1.05);
}

.video-thumbnail::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 80px;
    height: 80px;
    background: rgba(255, 255, 255, 0.2);
    border-radius: 50%;
    transition: var(--transition);
}

.video-thumbnail:hover::before {
    background: rgba(255, 255, 255, 0.3);
    transform: translate(-50%, -50%) scale(1.1);
}

.video-info {
    padding: 20px;
}

.video-title {
    font-size: 18px;
    font-weight: 700;
    margin-bottom: 8px;
    color: var(--text-primary);
    line-height: 1.4;
}

.video-desc {
    color: var(--text-secondary);
    line-height: 1.6;
    margin-bottom: 12px;
    font-size: 14px;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.video-stats {
    display: flex;
    justify-content: space-between;
    align-items: center;
    color: var(--text-light);
    font-size: 13px;
}

.video-teacher {
    display: inline-flex;
    align-items: center;
    gap: 5px;
    background: var(--bg-secondary);
    padding: 4px 10px;
    border-radius: 12px;
    font-size: 12px;
    color: var(--primary-color);
    font-weight: 500;
}

/* ===== 模态框 ===== */
.modal {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.6);
    z-index: 2000;
    align-items: center;
    justify-content: center;
    backdrop-filter: blur(5px);
    padding: 20px;
}

.modal.active {
    display: flex;
    animation: fadeIn 0.2s ease;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.modal-content {
    background: white;
    border-radius: 20px;
    width: 100%;
    max-width: 450px;
    max-height: 90vh;
    overflow-y: auto;
    padding: 40px;
    box-shadow: var(--shadow-xl);
    position: relative;
    animation: slideUp 0.3s ease;
}

@keyframes slideUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.admin-modal-content {
    max-width: 900px;
}

.content-modal-content {
    max-width: 800px;
}

.comments-modal-content {
    max-width: 700px;
    padding: 0;
    overflow: hidden;
}

.close-btn {
    position: absolute;
    top: 20px;
    right: 20px;
    font-size: 28px;
    cursor: pointer;
    color: var(--text-light);
    transition: var(--transition);
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 50%;
}

.close-btn:hover {
    background: var(--bg-secondary);
    color: var(--text-primary);
}

/* ===== 认证表单 ===== */
.auth-form h2 {
    text-align: center;
    margin-bottom: 30px;
    color: var(--text-primary);
}

.form-group {
    margin-bottom: 20px;
}

.form-label {
    display: block;
    margin-bottom: 8px;
    font-weight: 600;
    color: var(--text-primary);
    font-size: 14px;
}

.form-input,
.form-textarea,
.form-select {
    width: 100%;
    padding: 12px 16px;
    border: 2px solid var(--border-color);
    border-radius: 10px;
    font-size: 15px;
    transition: var(--transition);
    font-family: inherit;
}

.form-input:focus,
.form-textarea:focus,
.form-select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.1);
}

.form-textarea {
    resize: vertical;
    min-height: 100px;
}

.form-hint {
    display: block;
    margin-top: 5px;
    font-size: 12px;
    color: var(--text-light);
}

.auth-btn,
.upload-btn,
.btn-primary,
.btn-secondary {
    width: 100%;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    padding: 14px 24px;
    border: none;
    border-radius: 12px;
    cursor: pointer;
    font-size: 16px;
    font-weight: 600;
    transition: var(--transition);
    letter-spacing: 0.5px;
}

.auth-btn:hover,
.upload-btn:hover,
.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.btn-secondary {
    background: var(--bg-secondary);
    color: var(--text-primary);
}

.btn-secondary:hover {
    background: var(--border-color);
}

.auth-switch {
    text-align: center;
    margin-top: 20px;
    font-size: 14px;
    color: var(--text-secondary);
}

.auth-switch a {
    color: var(--primary-color);
    text-decoration: none;
    font-weight: 600;
}

.auth-switch a:hover {
    text-decoration: underline;
}

/* ===== 管理员面板 ===== */
.admin-login-form {
    text-align: center;
    padding: 40px 20px;
}

.admin-login-form h2 {
    margin-bottom: 30px;
}

.admin-tabs {
    display: flex;
    gap: 10px;
    margin-bottom: 30px;
    flex-wrap: wrap;
}

.admin-tab {
    padding: 10px 20px;
    border-radius: 25px;
    cursor: pointer;
    transition: var(--transition);
    background: var(--bg-secondary);
    font-weight: 600;
    border: 2px solid transparent;
    font-size: 14px;
}

.admin-tab.active {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.upload-form {
    background: var(--bg-secondary);
    padding: 30px;
    border-radius: 16px;
    margin-bottom: 30px;
    display: none;
}

.upload-form.active {
    display: block;
}

.upload-form h3 {
    margin-bottom: 25px;
    color: var(--text-primary);
    font-size: 20px;
}

.content-list {
    max-height: 400px;
    overflow-y: auto;
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 15px;
    background: white;
    margin-top: 20px;
}

.content-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px;
    border-bottom: 1px solid var(--border-color);
    transition: var(--transition);
    flex-wrap: wrap;
    gap: 10px;
}

.content-item:hover {
    background: var(--bg-secondary);
}

.content-item:last-child {
    border-bottom: none;
}

.content-actions {
    display: flex;
    gap: 8px;
}

.action-btn {
    padding: 6px 16px;
    border-radius: 20px;
    cursor: pointer;
    font-size: 13px;
    font-weight: 600;
    transition: var(--transition);
    border: none;
}

.edit-btn {
    background: var(--info-color);
    color: white;
}

.delete-btn {
    background: var(--danger-color);
    color: white;
}

.action-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-sm);
}

/* ===== 管理员按钮 ===== */
.admin-btn {
    position: fixed;
    bottom: 30px;
    right: 30px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    padding: 14px 28px;
    border-radius: 50px;
    cursor: pointer;
    box-shadow: var(--shadow-lg);
    transition: var(--transition);
    z-index: 999;
    font-weight: 600;
    letter-spacing: 0.5px;
    border: none;
    font-size: 14px;
}

.admin-btn:hover {
    transform: translateY(-3px) scale(1.02);
    box-shadow: var(--shadow-xl);
}

/* ===== 评论区 ===== */
.comments-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px;
    border-bottom: 1px solid var(--border-color);
}

.comments-header h2 {
    font-size: 20px;
}

.comments-container {
    max-height: 400px;
    overflow-y: auto;
    padding: 20px;
}

.comment {
    margin-bottom: 20px;
    padding-bottom: 20px;
    border-bottom: 1px solid var(--border-color);
}

.comment:last-child {
    border-bottom: none;
}

.comment-header {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 10px;
}

.comment-avatar {
    width: 36px;
    height: 36px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-weight: 600;
}

.comment-info {
    flex: 1;
}

.comment-author {
    font-weight: 600;
    color: var(--text-primary);
    font-size: 14px;
}

.comment-date {
    color: var(--text-light);
    font-size: 12px;
}

.comment-content {
    color: var(--text-secondary);
    line-height: 1.6;
    margin-left: 48px;
    font-size: 14px;
}

.comment-actions {
    display: flex;
    gap: 15px;
    margin-left: 48px;
    margin-top: 10px;
}

.comment-action {
    background: none;
    border: none;
    cursor: pointer;
    font-size: 13px;
    color: var(--text-light);
    transition: var(--transition);
}

.comment-action:hover {
    color: var(--primary-color);
}

.comment-form {
    padding: 20px;
    border-top: 1px solid var(--border-color);
}

.comment-input {
    width: 100%;
    padding: 12px 16px;
    border: 2px solid var(--border-color);
    border-radius: 10px;
    resize: vertical;
    min-height: 80px;
    font-family: inherit;
    font-size: 14px;
    margin-bottom: 10px;
    transition: var(--transition);
}

.comment-input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.1);
}

.comment-submit-btn {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    padding: 10px 24px;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    font-weight: 600;
    transition: var(--transition);
}

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

.comment-reply {
    margin-left: 48px;
    margin-top: 15px;
    padding-left: 20px;
    border-left: 2px solid var(--border-color);
}

/* ===== Toast 通知 ===== */
.toast {
    position: fixed;
    bottom: 30px;
    left: 50%;
    transform: translateX(-50%) translateY(100px);
    background: #333;
    color: white;
    padding: 14px 28px;
    border-radius: 12px;
    box-shadow: var(--shadow-lg);
    z-index: 3000;
    transition: transform 0.3s ease;
    font-size: 14px;
}

.toast.show {
    transform: translateX(-50%) translateY(0);
}

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

.toast.error {
    background: var(--danger-color);
}

.toast.warning {
    background: var(--warning-color);
}

.toast.info {
    background: var(--info-color);
}

/* ===== 加载指示器 ===== */
.loading {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(255, 255, 255, 0.9);
    z-index: 9999;
    align-items: center;
    justify-content: center;
}

.loading.active {
    display: flex;
}

.loading-spinner {
    width: 50px;
    height: 50px;
    border: 4px solid var(--border-color);
    border-top-color: var(--primary-color);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* ===== 内容详情模态框 ===== */
.content-detail {
    padding: 30px;
}

.content-detail-title {
    font-size: 24px;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 10px;
    line-height: 1.4;
}

.content-detail-subtitle {
    font-size: 16px;
    color: var(--text-secondary);
    margin-bottom: 20px;
}

.content-detail-body {
    color: var(--text-secondary);
    line-height: 1.8;
    font-size: 16px;
}

.content-detail-meta {
    display: flex;
    gap: 20px;
    margin-top: 30px;
    padding-top: 20px;
    border-top: 1px solid var(--border-color);
    color: var(--text-light);
    font-size: 14px;
}

/* ===== 响应式设计 ===== */
@media (max-width: 1024px) {
    .nav-container {
        padding: 15px 20px;
    }

    .nav-center {
        padding: 0 20px;
    }

    .culture-grid,
    .video-grid {
        grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
        gap: 20px;
    }

    .main-content {
        padding: 30px 20px;
    }
}

@media (max-width: 768px) {
    .nav-container {
        flex-wrap: wrap;
        gap: 10px;
    }

    .nav-center {
        order: 3;
        flex-basis: 100%;
        padding: 10px 0;
    }

    .nav-right {
        gap: 15px;
    }

    .nav-menu {
        gap: 5px;
    }

    .nav-item {
        padding: 8px 14px;
        font-size: 14px;
    }

    .culture-grid,
    .video-grid {
        grid-template-columns: 1fr;
    }

    .culture-title-main,
    .problems-title-main,
    .videos-title-main {
        font-size: 32px;
    }

    .modal-content {
        padding: 30px 20px;
        margin: 20px;
    }

    .admin-modal-content {
        margin: 10px;
        padding: 20px;
    }

    .admin-tabs {
        justify-content: center;
    }

    .search-container {
        max-width: 100%;
    }
}

@media (max-width: 480px) {
    .logo {
        font-size: 20px;
    }

    .nav-item {
        padding: 6px 12px;
        font-size: 13px;
    }

    .culture-title-main,
    .problems-title-main,
    .videos-title-main {
        font-size: 26px;
    }

    .main-content {
        padding: 20px 15px;
        margin-top: 70px;
    }

    .problem-header {
        flex-direction: column;
    }

    .problem-title {
        min-width: 100%;
    }
}

/* ===== 备案号底部 ===== */
.beian-footer {
    text-align: center;
    padding: 30px 20px;
    background: rgba(0, 0, 0, 0.3);
    margin-top: 60px;
}

.beian-footer a {
    color: rgba(255, 255, 255, 0.7);
    text-decoration: none;
    font-size: 14px;
    transition: var(--transition);
}

.beian-footer a:hover {
    color: white;
    text-decoration: underline;
}