/* 导航栏 */
        header {
            background-color: white;
            box-shadow: 0 2px 15px rgba(0, 0, 0, 0.05);
            position: sticky;
            top: 0;
            width: 100%;
            z-index: 1000;
        }
        
        nav {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 0px 0;
        }
        
        .logo {
            display: flex;
            align-items: center;
            font-size: 1.8rem;
            font-weight: 700;
            color: var(--primary);
            text-decoration: none;
        }
        
        .logo i {
            margin-right: 10px;
            color: var(--secondary);
        }
        
        .nav-links {
            display: flex;
            list-style: none;
            width: 60%!important; 
        }
        
        .nav-links li {
            margin-left: 30px;
        }
        
        .nav-links a {
            text-decoration: none;
            color: var(--dark);
            font-weight: 500;
            transition: var(--transition);
            padding: 5px 0;
            position: relative;
        }
        
        .nav-links a:hover {
            color: var(--primary);
        }
        
        .nav-links a::after {
            content: '';
            position: absolute;
            bottom: 0;
            left: 0;
            width: 0;
            height: 2px;
            background-color: var(--primary);
            transition: var(--transition);
        }
        
        .nav-links a:hover::after {
            width: 100%;
        }
        
        .nav-links a.active {
            color: var(--primary);
        }
        
        .nav-links a.active::after {
            width: 100%;
        }
        
        .nav-buttons {
            display: flex;
            align-items: center;
        }
        
        .nav-buttons .btn {
            margin-left: 15px;
        }
        
        
        
        /* 视频教程主布局 */
        .video-tutorials-container {
            display: flex;
            min-height: calc(100vh - 200px);
            padding-top: 30px;
            padding-bottom: 60px;
        }
                
        /* 左侧菜单 */
        .video-sidebar {
            width: 320px;
            background-color: white;
            border-radius: var(--border-radius);
            box-shadow: 0 5px 15px rgba(0, 0, 0, 0.05);
            padding: 25px 0;
            position: sticky;
            top: 100px;
            height: calc(100vh - 140px);
            overflow-y: auto;
            flex-shrink: 0;
        }
        
        .sidebar-header {
            padding: 0 25px 20px;
            border-bottom: 1px solid var(--light-gray);
            margin-bottom: 15px;
        }
        
        .sidebar-header h2 {
            font-size: 1.4rem;
            color: var(--dark);
            display: flex;
            align-items: center;
        }
        
        .sidebar-header h2 i {
            margin-right: 10px;
            color: var(--primary);
        }
        
        .sidebar-search {
            padding: 0 25px 20px;
            position: relative;
        }
        
        .sidebar-search input {
            width: 100%;
            padding: 10px 15px 10px 40px;
            border-radius: 8px;
            border: 1px solid var(--light-gray);
            font-size: 0.95rem;
            transition: var(--transition);
        }
        
        .sidebar-search input:focus {
            outline: none;
            border-color: var(--primary);
            box-shadow: 0 0 0 3px rgba(58, 134, 255, 0.1);
        }
        
        .sidebar-search i {
            position: absolute;
            left: 35px;
            top: 50%;
            transform: translateY(-50%);
            color: var(--gray);
        }
        
        .sidebar-menu {
            padding: 0 15px;
        }
        
        .video-category {
            margin-bottom: 20px;
        }
        
        .video-category-title {
            padding: 12px 10px;
            font-weight: 600;
            color: var(--dark);
            font-size: 1rem;
            display: flex;
            align-items: center;
            cursor: pointer;
            border-radius: 6px;
            transition: var(--transition);
            background-color: #f8f9fa;
        }
        
        .video-category-title:hover {
            background-color: rgba(58, 134, 255, 0.05);
            color: var(--primary);
        }
        
        .video-category-title i {
            margin-right: 10px;
            font-size: 0.9rem;
            color: var(--gray);
            transition: var(--transition);
        }
        
        .video-category-title:hover i {
            color: var(--primary);
        }
        
        .video-category-title .toggle-icon {
            margin-left: auto;
            font-size: 0.8rem;
            transition: var(--transition);
        }
        
        .video-category-title.active .toggle-icon {
            transform: rotate(90deg);
        }
        
        .video-list {
            padding-left: 30px;
            max-height: 0;
            overflow: hidden;
            transition: max-height 0.3s ease;
        }
        
        .video-category.active .video-list {
            max-height: 2000px;
        }
        
        .video-item {
            margin-bottom: 8px;
            padding: 2px;
        }
        
        .video-item a {
            display: flex;
            padding: 12px 15px;
            text-decoration: none;
            color: var(--gray);
            font-size: 0.95rem;
            border-radius: 6px;
            transition: var(--transition);
            position: relative;
            align-items: flex-start;
        }
        
        .video-item a:hover {
            background-color: rgba(58, 134, 255, 0.05);
            color: var(--primary);
        }
        
        .video-item a.active {
            background-color: rgba(58, 134, 255, 0.1);
            color: var(--primary);
            font-weight: 500;
        }
        
        .video-item a.active::before {
            content: '';
            position: absolute;
            left: 0;
            top: 0;
            bottom: 0;
            width: 3px;
            background-color: var(--primary);
            border-radius: 0 3px 3px 0;
        }
        
        .video-icon {
            width: 24px;
            height: 24px;
            background-color: rgba(58, 134, 255, 0.1);
            border-radius: 4px;
            display: flex;
            align-items: center;
            justify-content: center;
            margin-right: 12px;
            flex-shrink: 0;
            color: var(--primary);
            font-size: 0.8rem;
        }
        
        .video-info {
            flex: 1;
        }
        
        .video-title {
            font-weight: 500;
            margin-bottom: 4px;
            line-height: 1.3;
        }
        
        .video-duration {
            font-size: 0.8rem;
            color: var(--gray);
            display: flex;
            align-items: center;
        }
        
        .video-duration i {
            margin-right: 5px;
            font-size: 0.7rem;
        }
        
        .watched-badge {
            background-color: var(--primary);
            color: white;
            font-size: 0.7rem;
            padding: 2px 6px;
            border-radius: 10px;
            margin-left: 10px;
        }
        
        /* 右侧内容区域 */
        .video-content {
            flex: 1;
            margin-left: 30px;
            display: flex;
            flex-direction: column;
        }
        
        /* 视频播放器区域 */
        .video-player-container {
            background-color: white;
            border-radius: var(--border-radius);
            box-shadow: 0 5px 15px rgba(0, 0, 0, 0.05);
            overflow: hidden;
            margin-bottom: 30px;
        }
        
        .video-player-header {
            padding: 20px 30px;
            border-bottom: 1px solid var(--light-gray);
            background-color: #fdfdfd;
            display: flex;
            justify-content: space-between;
            align-items: center;
            flex-wrap: wrap;
            gap: 15px;
        }
        
        .video-player-header h2 {
            font-size: 1.5rem;
            color: var(--dark);
            display: flex;
            align-items: center;
        }
        
        .video-player-header h2 i {
            margin-right: 12px;
            color: var(--primary);
        }
        
        .video-actions {
            display: flex;
            gap: 10px;
        }
        
        .video-actions .btn {
            padding: 8px 16px;
            font-size: 0.9rem;
            display: flex;
            align-items: center;
            gap: 8px;
        }
        
        .video-player-wrapper {
            position: relative;
            background-color: #000;
            min-height: 400px;
        }
        
        .video-player {
            width: 100%;
            display: block;
            background-color: #000;
        }
        
        .video-placeholder {
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            height: 500px;
            padding: 40px;
            text-align: center;
            color: white;
            background: linear-gradient(135deg, #1a1a2e, #16213e);
        }
        
        .video-placeholder i {
            font-size: 5rem;
            color: rgba(255, 255, 255, 0.2);
            margin-bottom: 20px;
        }
        
        .video-placeholder h3 {
            font-size: 1.8rem;
            color: white;
            margin-bottom: 10px;
        }
        
        .video-placeholder p {
            max-width: 500px;
            margin-bottom: 30px;
            color: rgba(255, 255, 255, 0.7);
        }
        
        .video-controls {
            position: absolute;
            bottom: 0;
            left: 0;
            right: 0;
            background: linear-gradient(to top, rgba(0,0,0,0.8), transparent);
            padding: 20px;
            display: flex;
            justify-content: space-between;
            align-items: center;
            opacity: 0;
            transition: opacity 0.3s ease;
        }
        
        .video-player-wrapper:hover .video-controls {
            opacity: 1;
        }
        
        .control-left, .control-right {
            display: flex;
            gap: 15px;
            align-items: center;
        }
        
        .control-btn {
            background: rgba(255, 255, 255, 0.1);
            border: none;
            color: white;
            width: 40px;
            height: 40px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            cursor: pointer;
            transition: var(--transition);
        }
        
        .control-btn:hover {
            background: rgba(255, 255, 255, 0.2);
            transform: scale(1.1);
        }
        
        .progress-bar {
            flex: 1;
            height: 6px;
            background: rgba(255, 255, 255, 0.2);
            border-radius: 3px;
            margin: 0 20px;
            position: relative;
            cursor: pointer;
        }
        
        .progress-filled {
            position: absolute;
            top: 0;
            left: 0;
            height: 100%;
            background: var(--primary);
            border-radius: 3px;
            width: 0%;
        }
        
        .time-display {
            color: white;
            font-size: 0.9rem;
            min-width: 100px;
        }
        
        .volume-control {
            display: flex;
            align-items: center;
            gap: 10px;
        }
        
        .volume-slider {
            width: 80px;
            height: 4px;
            background: rgba(255, 255, 255, 0.2);
            border-radius: 2px;
            position: relative;
            cursor: pointer;
        }
        
        .volume-level {
            position: absolute;
            top: 0;
            left: 0;
            height: 100%;
            background: white;
            border-radius: 2px;
            width: 70%;
        }
        
        /* 视频详情区域 */
        .video-details {
            background-color: white;
            border-radius: var(--border-radius);
            box-shadow: 0 5px 15px rgba(0, 0, 0, 0.05);
            padding: 30px;
            margin-bottom: 30px;
        }
        
        .video-details-header {
            display: flex;
            justify-content: space-between;
            align-items: flex-start;
            margin-bottom: 20px;
            flex-wrap: wrap;
            gap: 15px;
        }
        
        .video-details-header h3 {
            font-size: 1.4rem;
            color: var(--dark);
        }
        
        .video-meta {
            display: flex;
            gap: 20px;
            color: var(--gray);
            font-size: 0.9rem;
        }
        
        .video-meta span {
            display: flex;
            align-items: center;
            gap: 6px;
        }
        
        .video-description {
            color: var(--gray);
            line-height: 1.7;
            margin-bottom: 25px;
        }
        
        .video-description h4 {
            color: var(--dark);
            margin-bottom: 10px;
            font-size: 1.1rem;
        }
        
        .video-tags {
            display: flex;
            flex-wrap: wrap;
            gap: 10px;
            margin-top: 20px;
        }
        
        .video-tag {
            background-color: rgba(58, 134, 255, 0.1);
            color: var(--primary);
            padding: 5px 12px;
            border-radius: 20px;
            font-size: 0.85rem;
            font-weight: 500;
        }
        
        /* 相关视频区域 */
        .related-videos {
            background-color: white;
            border-radius: var(--border-radius);
            box-shadow: 0 5px 15px rgba(0, 0, 0, 0.05);
            padding: 30px;
        }
        
        .related-videos h3 {
            font-size: 1.3rem;
            color: var(--dark);
            margin-bottom: 20px;
            display: flex;
            align-items: center;
        }
        
        .related-videos h3 i {
            margin-right: 10px;
            color: var(--primary);
        }
        
        .related-videos-list {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
            gap: 20px;
        }
        
        .related-video-card {
            border-radius: 8px;
            overflow: hidden;
            box-shadow: 0 3px 10px rgba(0, 0, 0, 0.08);
            transition: var(--transition);
            cursor: pointer;
        }
        
        .related-video-card:hover {
            transform: translateY(-5px);
            box-shadow: 0 10px 20px rgba(0, 0, 0, 0.12);
        }
        
        .related-video-thumbnail {
            height: 140px;
            background-color: #1a1a2e;
            position: relative;
            display: flex;
            align-items: center;
            justify-content: center;
        }
        
        .related-video-thumbnail i {
            color: white;
            font-size: 2.5rem;
            opacity: 0.7;
        }
        
        .related-video-duration {
            position: absolute;
            bottom: 10px;
            right: 10px;
            background: rgba(0, 0, 0, 0.7);
            color: white;
            padding: 3px 8px;
            border-radius: 4px;
            font-size: 0.8rem;
        }
        
        .related-video-info {
            padding: 15px;
        }
        
        .related-video-title {
            font-weight: 600;
            margin-bottom: 8px;
            color: var(--dark);
            line-height: 1.3;
            font-size: 0.95rem;
        }
        
        .related-video-meta {
            color: var(--gray);
            font-size: 0.85rem;
            display: flex;
            justify-content: space-between;
        }

        /* 响应式设计 */
        @media (max-width: 1200px) {
            .video-tutorials-container {
                flex-direction: column;
            }
            
            .video-sidebar {
                width: 100%;
                position: relative;
                top: 0;
                height: auto;
                max-height: 500px;
                margin-bottom: 30px;
                overflow-y: auto;
            }
            
            .video-content {
                margin-left: 0;
            }
            
            .video-player {
                height: 400px;
            }
            
            .video-placeholder {
                height: 400px;
            }
        }
        
        @media (max-width: 992px) {
            .nav-links {
                display: none;
            }
            
            .mobile-menu-toggle {
                display: block;
            }
            
            .page-header h1 {
                font-size: 2rem;
            }
            
            .related-videos-list {
                grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
            }
        }
        
        @media (max-width: 768px) {
            .video-actions {
                width: 100%;
                justify-content: space-between;
            }
            
            .video-actions .btn {
                flex: 1;
                justify-content: center;
            }
            
            .video-player {
                height: 300px;
            }
            
            .video-placeholder {
                height: 300px;
                padding: 20px;
            }
            
            .video-placeholder i {
                font-size: 3rem;
            }
            
            .video-placeholder h3 {
                font-size: 1.3rem;
            }
            
            .video-details-header {
                flex-direction: column;
            }
            
            .video-meta {
                flex-wrap: wrap;
            }
            
            .back-to-top {
                bottom: 20px;
                right: 20px;
                width: 45px;
                height: 45px;
            }
        }
        
        @media (max-width: 576px) {
            .video-sidebar {
                padding: 20px 0;
            }
            
            .sidebar-header, .sidebar-search {
                padding: 0 20px 15px;
            }
            
            .video-category-title, .video-item a {
                padding: 10px;
            }
            
            .page-header h1 {
                font-size: 1.5rem;
            }
            
            .video-player-header h2 {
                font-size: 1.2rem;
            }
            
            .video-actions .btn span {
                display: none;
            }
            
            .video-actions .btn i {
                margin-right: 0;
            }
            
            .control-left, .control-right {
                gap: 10px;
            }
            
            .progress-bar {
                margin: 0 10px;
            }
            
            .time-display {
                min-width: 70px;
            }
            
            .volume-slider {
                width: 60px;
            }
            
            .related-videos-list {
                grid-template-columns: 1fr;
            }
        }