/* ========== 方案4：骨架屏样式 ========== */
        .skeleton-loading {
            background: linear-gradient(90deg, #f0f0f0 25%, #e0e0e0 50%, #f0f0f0 75%);
            background-size: 200% 100%;
            animation: skeleton-wave 1.5s ease-in-out infinite;
            border-radius: 6px;
        }
        @keyframes skeleton-wave {
            0% { background-position: 200% 0; }
            100% { background-position: -200% 0; }
        }
        .skeleton-tabs {
            display: flex;
            gap: 8px;
            padding: 12px 16px;
            overflow: hidden;
        }
        .skeleton-tab {
            width: 70px;
            height: 60px;
            flex-shrink: 0;
        }
        .skeleton-list {
            padding: 16px;
        }
        .skeleton-item {
            display: flex;
            align-items: center;
            gap: 12px;
            padding: 12px;
            margin-bottom: 8px;
            background: #f8fafc;
            border-radius: 8px;
        }
        .skeleton-icon {
            width: 32px;
            height: 32px;
            flex-shrink: 0;
        }
        .skeleton-text {
            flex: 1;
        }
        .skeleton-title {
            height: 16px;
            width: 80%;
            margin-bottom: 8px;
        }
        .skeleton-subtitle {
            height: 12px;
            width: 50%;
        }
        
        /* ========== 基础样式重置 ========== */
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        
        /* ========== 页面布局 ========== */
        /* 禁止 body 滚动 */
        html, body {
            overflow: hidden;
            height: 100vh;
            height: 100dvh;  /* 动态视口高度，适配移动浏览器地址栏 */
        }
        
        .course-page {
            padding-top: 70px;
            height: 100vh;
            height: 100dvh;
            background: #f8fafc;
            overflow: hidden;
        }
        
        .course-container {
            display: flex;
            height: calc(100vh - 70px);
            height: calc(100dvh - 70px);
            max-height: calc(100vh - 70px);
            max-height: calc(100dvh - 70px);
            overflow: hidden;
        }
        
        /* ========== 左侧面板 ========== */
        .course-sidebar {
            width: 480px;
            min-width: 480px;
            display: flex;
            flex-direction: column;
            background: #ffffff;
            border-right: 1px solid #e2e8f0;
            overflow: hidden;
            transition: width 0.3s ease, min-width 0.3s ease;
            position: relative;
            box-shadow: 2px 0 8px rgba(0,0,0,0.05);
        }
        
        /* 侧边栏收起状态 */
        .course-sidebar.collapsed {
            width: 0;
            min-width: 0;
            border-right: none;
            overflow: visible; /* 允许按钮溢出显示 */
        }
        
        .course-sidebar.collapsed .sidebar-content {
            opacity: 0;
            pointer-events: none;
        }
        
        /* 侧边栏内容容器 */
        .sidebar-content {
            display: flex;
            flex-direction: column;
            height: 100%;
            width: 480px; /* 固定内容宽度 */
            transition: opacity 0.2s ease;
        }
        
        /* 侧边栏收缩按钮 - 展开状态：标题栏右侧 */
        .sidebar-collapse-btn {
            position: absolute;
            top: 16px;
            right: 16px;
            width: 36px;
            height: 36px;
            background: #ffffff;
            border: 1px solid #e2e8f0;
            border-radius: 8px;
            color: #64748b;
            cursor: pointer;
            display: flex;
            align-items: center;
            justify-content: center;
            transition: all 0.3s ease;
            z-index: 100;
        }
        
        .sidebar-collapse-btn:hover {
            background: #3b82f6;
            color: white;
            border-color: #3b82f6;
        }
        
        .sidebar-collapse-btn i {
            font-size: 14px;
            transition: all 0.3s ease;
        }
        
        /* 收缩状态时按钮样式 - 左下角圆形菜单按钮 */
        .course-sidebar.collapsed .sidebar-collapse-btn {
            position: fixed;
            top: auto;
            right: auto;
            left: 20px;
            bottom: 20px;
            border-radius: 50%;
            width: 56px;
            height: 56px;
            background: linear-gradient(135deg, #3b82f6 0%, #1d4ed8 100%);
            border: none;
            color: white;
            box-shadow: 0 4px 20px rgba(59, 130, 246, 0.4);
            z-index: 1000;
        }
        
        .course-sidebar.collapsed .sidebar-collapse-btn:hover {
            transform: scale(1.1);
            box-shadow: 0 6px 25px rgba(59, 130, 246, 0.5);
        }
        
        .course-sidebar.collapsed .sidebar-collapse-btn i {
            font-size: 20px;
        }
        
        /* ========== 侧边栏标题区域 ========== */
        .sidebar-header {
            padding: 16px 20px;
            background: linear-gradient(135deg, #eff6ff 0%, #f5f3ff 100%);
            border-bottom: 1px solid #e2e8f0;
            flex-shrink: 0;
            display: flex;
            align-items: center;
            justify-content: space-between;
        }
        
        .sidebar-title {
            font-size: 18px;
            font-weight: 700;
            color: #1e293b;
            display: flex;
            align-items: center;
            gap: 10px;
        }
        
        .sidebar-title i {
            font-size: 22px;
            color: #3b82f6;
        }
        
        /* ========== 课程按钮区域 ========== */
        .course-buttons {
            padding: 12px;
            display: flex;
            flex-direction: row;
            gap: 8px;
            border-bottom: 1px solid #e2e8f0;
            flex-shrink: 0;
        }
        
        .course-btn {
            display: flex;
            align-items: center;
            gap: 8px;
            padding: 10px 12px;
            border-radius: 10px;
            font-size: 13px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s ease;
            text-decoration: none;
            border: none;
            flex: 1;
        }
        
        .course-btn.free-btn {
            background: linear-gradient(135deg, #fb7299 0%, #ff85a8 100%);
            color: white;
            box-shadow: 0 4px 15px rgba(251, 114, 153, 0.3);
        }
        
        .course-btn.free-btn:hover {
            transform: translateY(-2px);
            box-shadow: 0 8px 25px rgba(251, 114, 153, 0.4);
        }
        
        .course-btn.paid-btn {
            background: linear-gradient(135deg, #3b82f6 0%, #1d4ed8 100%);
            color: white;
            box-shadow: 0 4px 15px rgba(59, 130, 246, 0.3);
        }
        
        .course-btn.paid-btn:hover {
            transform: translateY(-2px);
            box-shadow: 0 8px 25px rgba(59, 130, 246, 0.4);
        }
        
        .course-btn i {
            font-size: 16px;
        }
        
        .course-btn-text {
            flex: 1;
        }
        
        .course-btn-text span {
            display: block;
            font-size: 10px;
            font-weight: 400;
            opacity: 0.85;
            margin-top: 1px;
        }
        
        .course-btn .btn-arrow {
            font-size: 20px;
            opacity: 0.8;
        }
        
        /* ========== 课程列表区域 ========== */
        .course-list-section {
            display: flex;
            flex-direction: column;
            flex: 1;
            overflow: hidden;
        }
        
        .course-list-header {
            display: flex;
            align-items: center;
            justify-content: space-between;
            padding: 12px 16px;
            background: #f8fafc;
            border-bottom: 1px solid #e2e8f0;
            flex-shrink: 0;
        }
        
        .course-list-title {
            font-size: 14px;
            font-weight: 600;
            color: #3b82f6;
            display: flex;
            align-items: center;
            gap: 8px;
        }
        
        .course-list-title i {
            color: #3b82f6;
        }
        
        /* 目录Tab切换 - 5个一排 */
        .tabs-header {
            display: flex;
            padding: 12px;
            gap: 8px;
            background: #f1f5f9;
            border-bottom: 1px solid #e2e8f0;
            flex-shrink: 0;
        }
        
        .tab-btn {
            flex: 1;
            padding: 12px 6px;
            background: #ffffff;
            border: 1px solid #e2e8f0;
            border-radius: 10px;
            color: #64748b;
            font-size: 12px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s ease;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            gap: 5px;
            min-height: 80px;
        }
        
        .tab-btn i {
            font-size: 18px;
        }
        
        .tab-btn .tab-name {
            font-size: 12px;
            font-weight: 600;
            white-space: nowrap;
        }
        
        .tab-btn:hover {
            color: #3b82f6;
            background: #eff6ff;
            border-color: #3b82f6;
            transform: translateY(-2px);
        }
        
        .tab-btn.active {
            color: #ffffff;
            background: linear-gradient(135deg, #3b82f6 0%, #1d4ed8 100%);
            border-color: #3b82f6;
            box-shadow: 0 4px 15px rgba(59, 130, 246, 0.3);
        }
        
        .tab-btn .tab-status {
            font-size: 10px;
            padding: 2px 8px;
            border-radius: 8px;
            font-weight: 700;
        }
        
        .tab-btn .tab-status.free {
            background: #d1fae5;
            color: #059669;
        }
        
        .tab-btn .tab-status.locked {
            background: #fee2e2;
            color: #dc2626;
        }
        
        /* 课程图片Tab样式 */
        .tab-btn.tab-images .tab-status {
            background: #fef3c7;
            color: #d97706;
        }
        
        /* 课程信息 */
        .course-info {
            padding: 12px 16px;
            background: #f8fafc;
            border-bottom: 1px solid #e2e8f0;
            flex-shrink: 0;
        }
        
        .course-title {
            font-size: 14px;
            font-weight: 600;
            color: #1e293b;
            margin-bottom: 6px;
            display: flex;
            align-items: center;
            gap: 8px;
        }
        
        .course-title .badge {
            font-size: 10px;
            padding: 2px 6px;
            border-radius: 4px;
            font-weight: 500;
        }
        
        .badge-free {
            background: #10b981;
            color: white;
        }
        
        .badge-purchased {
            background: #3b82f6;
            color: white;
        }
        
        .course-meta {
            display: flex;
            align-items: center;
            gap: 12px;
            font-size: 12px;
            color: #64748b;
        }
        
        .course-meta i {
            margin-right: 4px;
        }
        
        .progress-bar {
            height: 3px;
            background: #e2e8f0;
            border-radius: 2px;
            margin-top: 10px;
            overflow: hidden;
        }
        
        .progress-fill {
            height: 100%;
            background: linear-gradient(90deg, #10b981, #059669);
            border-radius: 2px;
            transition: width 0.3s ease;
        }
        
        /* 视频列表 */
        .video-list-container {
            flex: 1;
            overflow-y: auto;
            padding: 8px;
            background: #ffffff;
        }
        
        .video-list-container::-webkit-scrollbar {
            width: 6px;
        }
        
        .video-list-container::-webkit-scrollbar-track {
            background: #f1f5f9;
        }
        
        .video-list-container::-webkit-scrollbar-thumb {
            background: #cbd5e1;
            border-radius: 3px;
        }
        
        .video-item {
            display: flex;
            align-items: center;
            gap: 10px;
            padding: 10px;
            border-radius: 8px;
            cursor: pointer;
            transition: all 0.2s ease;
            margin-bottom: 4px;
        }
        
        .video-item:hover {
            background: #eff6ff;
        }
        
        .video-item.active {
            background: #dbeafe;
            border-left: 3px solid #3b82f6;
        }
        
        .video-item.locked {
            opacity: 0.5;
        }
        
        .video-item-status {
            width: 28px;
            height: 28px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            flex-shrink: 0;
            font-size: 11px;
        }
        
        .video-item-status.watched {
            background: #d1fae5;
            color: #059669;
        }
        
        .video-item-status.playing {
            background: linear-gradient(135deg, #3b82f6, #1d4ed8);
            color: white;
            animation: pulse-glow 2s infinite;
        }
        
        @keyframes pulse-glow {
            0%, 100% { box-shadow: 0 0 0 0 rgba(59, 130, 246, 0.4); }
            50% { box-shadow: 0 0 0 8px rgba(59, 130, 246, 0); }
        }
        
        .video-item-status.unwatched {
            background: #f1f5f9;
            color: #64748b;
            border: 1px solid #e2e8f0;
        }
        
        .video-item-status.locked-icon {
            background: #fee2e2;
            color: #dc2626;
        }
        
        .video-item-info {
            flex: 1;
            min-width: 0;
        }
        
        .video-item-name {
            font-size: 13px;
            color: #1e293b;
            white-space: nowrap;
            overflow: hidden;
            text-overflow: ellipsis;
        }
        
        .video-item-duration {
            font-size: 11px;
            color: #64748b;
            margin-top: 2px;
        }
        
        .video-item-badge {
            font-size: 10px;
            padding: 2px 6px;
            border-radius: 4px;
            background: #d1fae5;
            color: #059669;
        }
        
        /* 课程图片列表 */
        .image-list-container {
            flex: 1;
            overflow-y: auto;
            padding: 12px;
            background: #ffffff;
            border-radius: 8px;
        }
        
        .image-list-title {
            text-align: center;
            font-size: 16px;
            font-weight: 700;
            color: #1e293b;
            padding: 12px;
            background: #eff6ff;
            border-radius: 8px;
            margin-bottom: 12px;
        }
        
        .image-search-box {
            margin-bottom: 12px;
            position: relative;
        }
        
        .image-search-box input {
            width: 100%;
            padding: 10px 12px 10px 36px;
            background: #ffffff;
            border: 1px solid #e2e8f0;
            border-radius: 8px;
            color: #1e293b;
            font-size: 14px;
            outline: none;
            transition: all 0.2s;
        }
        
        .image-search-box input:focus {
            border-color: #3b82f6;
            box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
        }
        
        .image-search-box input::placeholder {
            color: #94a3b8;
        }
        
        .image-search-box i {
            position: absolute;
            left: 12px;
            top: 50%;
            transform: translateY(-50%);
            color: #64748b;
        }
        
        .image-grid {
            display: flex;
            flex-direction: column;
            gap: 12px;
        }
        
        .image-card {
            background: #ffffff;
            border: 1px solid #e2e8f0;
            border-radius: 12px;
            overflow: hidden;
            cursor: pointer;
            transition: all 0.3s ease;
        }
        
        .image-card:hover {
            border-color: #3b82f6;
            transform: translateY(-2px);
            box-shadow: 0 8px 25px rgba(59, 130, 246, 0.15);
        }
        
        .image-card img {
            width: 100%;
            height: auto;
            display: block;
        }
        
        .image-card .image-title {
            padding: 10px 12px;
            font-size: 13px;
            color: #1e293b;
            border-top: 1px solid #e2e8f0;
            background: #f8fafc;
        }
        
        /* 图片弹窗 */
        .image-modal {
            display: none;
            position: fixed;
            top: 0;
            left: 0;
            right: 0;
            bottom: 0;
            background: rgba(255, 255, 255, 0.25);
            backdrop-filter: blur(12px);
            -webkit-backdrop-filter: blur(12px);
            z-index: 10000;
            justify-content: center;
            align-items: center;
            padding: 20px;
        }
        
        .image-modal.show {
            display: flex;
        }
        
        .image-modal img {
            max-width: 80%;
            max-height: 75vh;
            object-fit: contain;
            border-radius: 8px;
            box-shadow: 0 8px 32px rgba(0, 0, 0, 0.2);
        }
        
        .image-modal .modal-close {
            position: absolute;
            top: 20px;
            right: 20px;
            width: 44px;
            height: 44px;
            background: rgba(0, 0, 0, 0.1);
            border: none;
            border-radius: 50%;
            color: #374151;
            font-size: 20px;
            cursor: pointer;
            transition: all 0.2s;
        }
        
        .image-modal .modal-close:hover {
            background: rgba(0, 0, 0, 0.2);
            color: #1f2937;
        }
        
        .image-modal .modal-nav {
            position: absolute;
            top: 50%;
            transform: translateY(-50%);
            width: 50px;
            height: 50px;
            background: rgba(0, 0, 0, 0.1);
            border: none;
            border-radius: 50%;
            color: #374151;
            font-size: 20px;
            cursor: pointer;
            transition: all 0.2s;
        }
        
        .image-modal .modal-nav:hover {
            background: rgba(0, 0, 0, 0.2);
            color: #1f2937;
        }
        
        .image-modal .modal-nav.prev {
            left: 20px;
        }
        
        .image-modal .modal-nav.next {
            right: 20px;
        }
        
        .image-modal .modal-counter {
            position: absolute;
            bottom: 20px;
            left: 50%;
            transform: translateX(-50%);
            color: #374151;
            font-size: 14px;
            background: rgba(255, 255, 255, 0.9);
            border: 1px solid rgba(0, 0, 0, 0.1);
            padding: 8px 16px;
            border-radius: 20px;
        }
        
        /* ========== 右侧主内容区 ========== */
        .course-main {
            flex: 1;
            display: flex;
            flex-direction: column;
            padding: 16px;
            padding-left: 24px;
            overflow: hidden;
            transition: padding-left 0.3s ease;
        }
        
        /* 侧边栏收起时，减少左边padding */
        .course-sidebar.collapsed + .course-main {
            padding-left: 16px;
        }
        
        /* 视频播放区域 */
        .video-section {
            flex: 1;
            display: flex;
            flex-direction: column;
            background: #ffffff;
            border-radius: 0;
            border: 1px solid #e2e8f0;
            overflow: hidden;
            min-height: 0;  /* 关键：允许 flex 子元素收缩 */
            box-shadow: 0 4px 15px rgba(0,0,0,0.08);
        }
        
        .video-container {
            position: relative;
            width: 100%;
            padding-top: 56.25%;  /* 强制 16:9 比例 (9/16 = 56.25%) */
            background: #1e293b;
            flex-shrink: 0;  /* 不允许收缩 */
        }
        
        .video-container video,
        .video-container .plyr {
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
        }
        
        .video-container video {
            object-fit: contain;  /* 保持比例，完整显示 */
        }
        
        /* ========== 视频水印（防录屏） ========== */
        .video-watermark {
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            pointer-events: none;
            z-index: 10;
            overflow: hidden;
            display: none;  /* 默认隐藏，播放时显示 */
        }
        
        .video-watermark.active {
            display: block;
        }
        
        .watermark-content {
            position: absolute;
            width: 200%;
            height: 200%;
            top: -50%;
            left: -50%;
            display: flex;
            flex-wrap: wrap;
            align-content: flex-start;
            transform: rotate(-25deg);
            animation: watermarkMove 60s linear infinite;
        }
        
        .watermark-item {
            padding: 40px 60px;
            font-size: 14px;
            color: rgba(255, 255, 255, 0.08);
            white-space: nowrap;
            user-select: none;
            font-weight: 500;
            letter-spacing: 1px;
        }
        
        @keyframes watermarkMove {
            0% { transform: rotate(-25deg) translateX(0) translateY(0); }
            100% { transform: rotate(-25deg) translateX(-100px) translateY(-100px); }
        }
        
        /* 滚动提示条 */
        .video-notice-bar {
            position: absolute;
            bottom: 60px;
            left: 0;
            width: 100%;
            height: 28px;
            background: linear-gradient(90deg, transparent, rgba(0,0,0,0.6), transparent);
            display: none;
            align-items: center;
            justify-content: center;
            z-index: 11;
            pointer-events: none;
        }
        
        .video-notice-bar.active {
            display: flex;
        }
        
        .notice-text {
            color: rgba(255, 255, 255, 0.7);
            font-size: 12px;
            white-space: nowrap;
            animation: noticeScroll 15s linear infinite;
        }
        
        @keyframes noticeScroll {
            0% { transform: translateX(100%); }
            100% { transform: translateX(-100%); }
        }
        
        /* ========== 移动端触摸反馈 ========== */
        .video-touch-feedback {
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            width: 80px;
            height: 80px;
            background: rgba(0, 0, 0, 0.6);
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            color: white;
            font-size: 32px;
            opacity: 0;
            pointer-events: none;
            z-index: 20;
            transition: opacity 0.2s;
        }
        
        .video-touch-feedback.show {
            opacity: 1;
        }
        
        .video-touch-feedback.left {
            left: 25%;
        }
        
        .video-touch-feedback.right {
            left: 75%;
        }
        
        .video-touch-feedback .seek-text {
            font-size: 14px;
            margin-top: 4px;
        }
        
        /* 进度提示 */
        .video-seek-indicator {
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            background: rgba(0, 0, 0, 0.75);
            padding: 12px 24px;
            border-radius: 8px;
            color: white;
            font-size: 16px;
            font-weight: 600;
            opacity: 0;
            pointer-events: none;
            z-index: 21;
            transition: opacity 0.2s;
        }
        
        .video-seek-indicator.show {
            opacity: 1;
        }
        
        .video-placeholder {
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            background: #ffffff;
            border: 1px solid #e2e8f0;
            z-index: 1;
            overflow: hidden;  /* 防止内容溢出 */
        }
        
        .placeholder-content {
            text-align: center;
            padding: 20px;
            animation: fadeInUp 0.6s ease;
            max-height: 100%;
            overflow: auto;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
        }
        
        .placeholder-icon {
            font-size: clamp(40px, 8vw, 70px);  /* 响应式图标大小 */
            color: #3b82f6;
            margin-bottom: 16px;
            animation: float 3s ease-in-out infinite;
            flex-shrink: 0;
        }
        
        .placeholder-title {
            font-size: clamp(20px, 4vw, 28px);  /* 响应式标题大小 */
            font-weight: 700;
            color: #1e293b;
            margin: 0 0 8px 0;
            flex-shrink: 0;
        }
        
        .placeholder-subtitle {
            font-size: clamp(14px, 2.5vw, 18px);  /* 响应式副标题大小 */
            color: #64748b;
            margin: 0 0 20px 0;
            font-weight: 500;
            flex-shrink: 0;
        }
        
        .placeholder-features {
            display: flex;
            gap: 16px;
            justify-content: center;
            margin-bottom: 20px;
            flex-wrap: wrap;
            flex-shrink: 0;
        }
        
        .feature-item {
            display: flex;
            flex-direction: column;
            align-items: center;
            gap: 6px;
            color: #475569;
            font-size: 13px;
            padding: 12px 16px;
            border-radius: 10px;
            background: #f1f5f9;
            border: 1px solid #e2e8f0;
            transition: all 0.3s ease;
        }
        
        .feature-item:hover {
            background: #e0f2fe;
            border-color: #93c5fd;
            transform: translateY(-4px);
        }
        
        .feature-item i {
            font-size: 22px;
            color: #3b82f6;
        }
        
        .placeholder-hint {
            display: inline-flex;
            align-items: center;
            gap: 8px;
            color: #d97706;
            font-size: 14px;
            padding: 10px 20px;
            background: #fef3c7;
            border-radius: 8px;
            border: 1px solid #fcd34d;
            flex-shrink: 0;
        }
        
        .placeholder-hint i {
            font-size: 16px;
            animation: pointLeft 1.5s ease-in-out infinite;
        }
        
        @keyframes fadeInUp {
            from {
                opacity: 0;
                transform: translateY(30px);
            }
            to {
                opacity: 1;
                transform: translateY(0);
            }
        }
        
        @keyframes float {
            0%, 100% { transform: translateY(0); }
            50% { transform: translateY(-10px); }
        }
        
        @keyframes pointLeft {
            0%, 100% { transform: translateX(0); }
            50% { transform: translateX(-8px); }
        }
        
        .video-info {
            padding: 16px 20px;
            background: #f8fafc;
            border-bottom: 1px solid #e2e8f0;
            flex-shrink: 0;
            display: flex;
            justify-content: space-between;
            align-items: center;
        }
        
        .video-info-left {
            flex: 1;
        }
        
        .video-info-right {
            display: flex;
            justify-content: flex-end;
        }
        
        .video-title {
            font-size: 18px;
            font-weight: 600;
            color: #1e293b;
            margin: 0 0 6px 0;
        }
        
        .video-meta {
            font-size: 13px;
            color: #64748b;
        }
        
        .btn-contact-teacher {
            display: inline-flex;
            align-items: center;
            justify-content: center;
            gap: 8px;
            padding: 12px 28px;
            background: linear-gradient(135deg, #07c160 0%, #06ad56 100%);
            color: white;
            border: none;
            border-radius: 24px;
            font-size: 15px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.2s ease;
            box-shadow: 0 3px 12px rgba(7, 193, 96, 0.35);
            flex-shrink: 0;
        }
        
        .btn-contact-teacher:hover {
            transform: translateY(-2px);
            box-shadow: 0 6px 18px rgba(7, 193, 96, 0.45);
        }
        
        .btn-contact-teacher i {
            font-size: 18px;
        }
        
        /* 购买提示遮罩 - 白色清爽风格 */
        .purchase-prompt {
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background: linear-gradient(180deg, #f8fafc 0%, #f1f5f9 100%);
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            color: #1e293b;
            text-align: center;
            padding: 30px 20px;
            z-index: 2;
        }
        
        .purchase-prompt i.fa-lock {
            font-size: 42px;
            color: #f59e0b;
            margin-bottom: 16px;
            filter: drop-shadow(0 2px 6px rgba(245, 158, 11, 0.25));
        }
        
        .purchase-prompt h3 {
            font-size: 20px;
            font-weight: 600;
            color: #1e293b;
            margin: 0 0 8px 0;
        }
        
        .purchase-prompt p {
            color: #64748b;
            font-size: 13px;
            margin-bottom: 16px;
        }
        
        .purchase-prompt .price {
            font-size: 36px;
            font-weight: 700;
            color: #ea580c;
            margin: 12px 0;
        }
        
        .purchase-prompt .original-price {
            font-size: 14px;
            color: #94a3b8;
            text-decoration: line-through;
            margin-left: 6px;
        }
        
        .purchase-prompt .btn-purchase {
            padding: 12px 32px;
            font-size: 15px;
            font-weight: 600;
            background: linear-gradient(135deg, #3b82f6 0%, #1d4ed8 100%);
            color: white;
            border: none;
            border-radius: 10px;
            cursor: pointer;
            transition: all 0.2s ease;
            margin-top: 12px;
            display: inline-flex;
            align-items: center;
            gap: 8px;
            box-shadow: 0 4px 12px rgba(59, 130, 246, 0.25);
        }
        
        .purchase-prompt .btn-purchase:hover {
            transform: translateY(-1px);
            box-shadow: 0 6px 16px rgba(59, 130, 246, 0.35);
        }
        
        /* 管理员工具栏 */
        .admin-bar {
            background: #fffbeb;
            border-top: 1px solid #e2e8f0;
            border-bottom: 1px solid #fcd34d;
            padding: 10px 16px;
            display: flex;
            align-items: center;
            justify-content: space-between;
        }
        
        .admin-bar span {
            color: #b45309;
            font-size: 14px;
        }
        
        .btn-sync {
            padding: 8px 20px;
            background: linear-gradient(135deg, #3b82f6, #1d4ed8);
            color: white;
            border: none;
            border-radius: 20px;
            cursor: pointer;
            font-size: 14px;
            transition: all 0.2s;
        }
        
        .btn-sync:hover {
            transform: translateY(-1px);
            box-shadow: 0 4px 15px rgba(59, 130, 246, 0.4);
        }
        
        .btn-sync:disabled {
            background: #94a3b8;
            cursor: not-allowed;
            transform: none;
            box-shadow: none;
        }
        
        /* 空状态 */
        .empty-state {
            text-align: center;
            padding: 40px 20px;
            color: #64748b;
        }
        
        .empty-state i {
            font-size: 48px;
            color: #cbd5e1;
            margin-bottom: 16px;
        }
        
        /* 加载状态 */
        .loading {
            text-align: center;
            padding: 40px;
            color: #64748b;
        }
        
        .loading i {
            font-size: 32px;
            color: #3b82f6;
            animation: spin 1s linear infinite;
        }
        
        @keyframes spin {
            from { transform: rotate(0deg); }
            to { transform: rotate(360deg); }
        }
        
        /* ========== 侧边栏遮罩层 ========== */
        .sidebar-overlay {
            display: none;
            position: fixed;
            top: 70px;
            left: 0;
            right: 0;
            bottom: 0;
            background: rgba(15, 23, 42, 0.6);
            backdrop-filter: blur(2px);
            z-index: 999;
            opacity: 0;
            transition: opacity 0.3s ease;
        }
        
        .sidebar-overlay.show {
            display: block;
            opacity: 1;
        }
        
        /* ========== 响应式 ========== */
        @media (max-width: 1200px) {
            .course-sidebar {
                width: 440px;
                min-width: 440px;
            }
            
            .sidebar-content {
                width: 440px;
            }
        }
        
        @media (max-width: 900px) {
            /* 保持左右布局，不要上下布局 */
            .course-container {
                flex-direction: row;
                position: relative;
            }
            
            /* 侧边栏变成固定定位的抽屉 */
            .course-sidebar {
                position: fixed;
                left: 0;
                top: 60px;
                bottom: 0;
                width: 85%;
                max-width: 400px;
                min-width: 0;
                z-index: 1000;
                box-shadow: 4px 0 20px rgba(0,0,0,0.3);
                transform: translateX(0);
                transition: transform 0.3s ease;
                border-right: 1px solid #e2e8f0;
            }
            
            .sidebar-content {
                width: 100%;
            }
            
            /* 隐藏状态：向左滑出屏幕 */
            .course-sidebar.collapsed {
                transform: translateX(-100%);
                box-shadow: none;
            }
            
            /* 侧边栏展开时的收起按钮 */
            .sidebar-collapse-btn {
                width: 36px;
                height: 36px;
            }
            
            .sidebar-collapse-btn i {
                font-size: 14px;
            }
            
            /* 侧边栏收起时的菜单按钮 - 固定左下角 */
            .course-sidebar.collapsed .sidebar-collapse-btn {
                position: fixed;
                left: 16px;
                bottom: 16px;
                width: 56px;
                height: 56px;
                z-index: 1001;
                box-shadow: 0 4px 20px rgba(59, 130, 246, 0.5);
            }
            
            .course-sidebar.collapsed .sidebar-collapse-btn i {
                font-size: 20px;
            }
            
            /* 视频区域占满全屏 */
            .course-main {
                flex: 1;
                width: 100%;
                padding: 12px;
            }
            
            .video-list-container {
                max-height: none;
            }
            
            /* 遮罩层位置调整 */
            .sidebar-overlay {
                top: 60px;
            }
            
            /* 视频容器保持 16:9 比例 */
            .video-container {
                padding-top: 56.25%;
            }
        }
        
        @media (max-width: 600px) {
            .course-page {
                padding-top: 60px;
                height: 100vh;
                height: 100dvh;
            }
            
            .course-container {
                height: calc(100vh - 60px);
                height: calc(100dvh - 60px);
                max-height: calc(100vh - 60px);
                max-height: calc(100dvh - 60px);
            }
            
            /* 视频容器保持 16:9 比例 */
            .video-container {
                padding-top: 56.25%;
            }
            
            /* ====== 简化侧边栏，腾出更多空间给目录 ====== */
            
            /* 隐藏标题栏 */
            .sidebar-header {
                display: none;
            }
            
            /* 课程按钮更紧凑 - 隐藏小字 */
            .course-buttons {
                padding: 6px;
                gap: 6px;
                flex-direction: row;
            }
            
            .course-btn {
                padding: 8px 12px;
                font-size: 12px;
                border-radius: 8px;
            }
            
            .course-btn i {
                font-size: 14px;
            }
            
            /* 移动端隐藏按钮下方小字 */
            .course-btn-text span {
                display: none;
            }
            
            .course-btn .btn-arrow {
                font-size: 14px;
            }
            
            /* Tab 按钮更紧凑（横向排列） */
            .tabs-header {
                padding: 6px 8px;
                gap: 4px;
                flex-wrap: nowrap;
                overflow-x: auto;
            }
            
            .tab-btn {
                flex: 0 0 auto;
                min-width: auto;
                padding: 6px 10px;
                min-height: auto;
                flex-direction: row;
                gap: 4px;
            }
            
            .tab-btn i {
                font-size: 12px;
            }
            
            .tab-btn .tab-name {
                font-size: 11px;
            }
            
            .tab-btn .tab-status {
                font-size: 9px;
                padding: 1px 4px;
            }
            
            /* 课程信息更紧凑 */
            .course-info {
                padding: 6px 10px;
            }
            
            .course-title {
                font-size: 12px;
            }
            
            .course-meta {
                font-size: 10px;
                gap: 8px;
            }
            
            .progress-bar {
                height: 3px;
                margin-top: 4px;
            }
            
            /* 视频列表更紧凑 */
            .video-list-container {
                padding: 4px 0;
            }
            
            .chapter-header {
                padding: 6px 10px;
                font-size: 11px;
            }
            
            .video-item {
                padding: 8px 10px;
            }
            
            .video-item-name {
                font-size: 12px;
            }
            
            .course-main {
                padding: 10px;
            }
            
            .video-info {
                padding: 10px 12px;
            }
            
            .video-title {
                font-size: 14px;
            }
            
            /* placeholder 移动端优化 - 极简化 */
            .placeholder-content {
                padding: 12px;
            }
            
            .placeholder-icon {
                font-size: 40px;
                margin-bottom: 8px;
            }
            
            .placeholder-title {
                font-size: 18px;
                margin-bottom: 4px;
            }
            
            .placeholder-subtitle {
                font-size: 13px;
                margin-bottom: 12px;
            }
            
            /* 移动端隐藏功能特性列表 */
            .placeholder-features {
                display: none;
            }
            
            .placeholder-hint {
                font-size: 12px;
                padding: 8px 12px;
            }
            
            /* 购买提示移动端优化 - 缩小尺寸 */
            .purchase-prompt {
                padding: 16px 12px;
            }
            
            .purchase-prompt i.fa-lock {
                font-size: 28px;
                margin-bottom: 10px;
            }
            
            .purchase-prompt h3 {
                font-size: 16px;
                margin-bottom: 4px;
            }
            
            .purchase-prompt p {
                font-size: 12px;
                margin-bottom: 10px;
            }
            
            .purchase-prompt .price {
                font-size: 28px;
                margin: 8px 0;
            }
            
            .purchase-prompt .original-price {
                font-size: 12px;
            }
            
            .purchase-prompt .btn-purchase {
                padding: 10px 24px;
                font-size: 14px;
            }
            
            /* 确保页面在一屏内显示 */
            .course-main {
                padding: 8px;
                overflow: hidden;
            }
            
            .video-section {
                height: 100%;
                display: flex;
                flex-direction: column;
            }
        }
        
        /* 购买弹窗 */
        .purchase-modal {
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background: rgba(15, 23, 42, 0.8);
            backdrop-filter: blur(10px);
            display: flex;
            align-items: center;
            justify-content: center;
            z-index: 1000;
            opacity: 0;
            visibility: hidden;
            transition: all 0.3s ease;
        }
        
        .purchase-modal.show {
            opacity: 1;
            visibility: visible;
        }
        
        .purchase-modal-content {
            background: #ffffff;
            border: 1px solid #e2e8f0;
            border-radius: 24px;
            padding: 28px;
            max-width: 700px;
            width: 95%;
            transform: translateY(20px);
            transition: transform 0.3s ease;
            box-shadow: 0 20px 50px rgba(0,0,0,0.2);
        }
        
        #courseOptions {
            display: grid;
            grid-template-columns: repeat(4, 1fr);
            gap: 10px;
        }
        
        .purchase-modal.show .purchase-modal-content {
            transform: translateY(0);
        }
        
        .purchase-modal h3 {
            font-size: 24px;
            color: #1e293b;
            margin: 0 0 24px;
            text-align: center;
        }
        
        .course-option {
            background: #f8fafc;
            border: 2px solid #e2e8f0;
            border-radius: 10px;
            padding: 12px 8px;
            cursor: pointer;
            transition: all 0.3s ease;
            display: flex;
            flex-direction: column;
            align-items: center;
            text-align: center;
            gap: 6px;
        }
        
        .course-option:hover {
            background: #eff6ff;
            border-color: #93c5fd;
            transform: translateY(-2px);
        }
        
        .course-option.selected {
            background: #dbeafe;
            border-color: #3b82f6;
        }
        
        .course-option-header {
            display: none;
        }
        
        .course-option-title {
            font-size: 13px;
            font-weight: 600;
            color: #1e293b;
            line-height: 1.3;
        }
        
        .course-option-badge {
            display: flex;
            justify-content: center;
            min-height: 20px;
        }
        
        .course-option-price {
            font-size: 18px;
            font-weight: 700;
            color: #f97316;
        }
        
        .course-option-meta {
            font-size: 11px;
            color: #64748b;
            line-height: 1.4;
        }
        
        .course-option .badge {
            font-size: 11px;
            padding: 2px 8px;
            border-radius: 6px;
            margin-left: 8px;
        }
        
        .btn-confirm-purchase {
            width: 100%;
            padding: 16px;
            background: linear-gradient(135deg, #3b82f6 0%, #1d4ed8 100%);
            color: white;
            border: none;
            border-radius: 12px;
            font-size: 16px;
            font-weight: 600;
            cursor: pointer;
            margin-top: 20px;
            transition: all 0.3s ease;
        }
        
        .btn-confirm-purchase:hover {
            transform: translateY(-2px);
            box-shadow: 0 8px 25px rgba(59, 130, 246, 0.4);
        }
        
        .btn-close-modal {
            position: absolute;
            top: 16px;
            right: 16px;
            width: 36px;
            height: 36px;
            background: #f1f5f9;
            border: none;
            border-radius: 50%;
            color: #64748b;
            cursor: pointer;
            transition: all 0.2s;
        }
        
        .btn-close-modal:hover {
            background: #e2e8f0;
            color: #1e293b;
        }
        
        /* 微信二维码弹窗 */
        .wechat-modal {
            display: none;
            position: fixed;
            top: 0;
            left: 0;
            right: 0;
            bottom: 0;
            background: rgba(0, 0, 0, 0.6);
            z-index: 10000;
            justify-content: center;
            align-items: center;
        }
        .wechat-modal.show {
            display: flex;
        }
        .wechat-modal-content {
            position: relative;
            background: white;
            border-radius: 12px;
            overflow: hidden;
            box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
            padding: 16px;
        }
        .wechat-modal-content img {
            display: block;
            max-width: 390px;
            max-height: 85vh;
            border-radius: 8px;
        }
        .wechat-modal-close {
            position: absolute;
            top: 8px;
            right: 8px;
            width: 28px;
            height: 28px;
            background: rgba(0, 0, 0, 0.5);
            border: none;
            border-radius: 50%;
            color: white;
            font-size: 12px;
            cursor: pointer;
            z-index: 1;
            display: flex;
            align-items: center;
            justify-content: center;
            transition: background 0.2s;
        }
        .wechat-modal-close:hover {
            background: rgba(0, 0, 0, 0.7);
        }
        @media (max-width: 600px) {
            .wechat-modal-content img {
                max-width: 320px;
            }
            .btn-contact-teacher {
                padding: 6px 12px;
                font-size: 12px;
            }
            .btn-contact-teacher span {
                display: none;
            }
        }

        /* ==================== Plyr 播放器自定义样式 ==================== */
        /* 加大控制条 */
        .plyr__controls {
            padding: 16px !important;
            font-size: 16px !important;
        }
        
        /* 加大按钮 */
        .plyr__control {
            padding: 10px !important;
        }
        
        .plyr__control svg {
            width: 22px !important;
            height: 22px !important;
        }
        
        /* 加大中心播放按钮 */
        .plyr__control--overlaid {
            padding: 25px !important;
        }
        
        .plyr__control--overlaid svg {
            width: 36px !important;
            height: 36px !important;
        }
        
        /* 加粗进度条 */
        .plyr__progress input[type=range] {
            height: 8px !important;
        }
        
        .plyr__progress__buffer {
            height: 8px !important;
        }
        
        /* 进度条滑块加大 */
        .plyr__progress input[type=range]::-webkit-slider-thumb {
            width: 18px !important;
            height: 18px !important;
        }
        
        .plyr__progress input[type=range]::-moz-range-thumb {
            width: 18px !important;
            height: 18px !important;
        }
        
        /* 音量滑块加大 */
        .plyr__volume input[type=range]::-webkit-slider-thumb {
            width: 16px !important;
            height: 16px !important;
        }
        
        .plyr__volume input[type=range]::-moz-range-thumb {
            width: 16px !important;
            height: 16px !important;
        }
        
        /* 倍速菜单样式 */
        .plyr__menu__container {
            font-size: 15px !important;
        }
        
        .plyr__menu__container [role=menuitemradio] {
            padding: 10px 12px !important;
        }
        
        /* 控制栏按钮更明显 */
        .plyr__control {
            color: #fff !important;
            opacity: 1 !important;
        }
        
        .plyr__control:hover {
            background: rgba(59, 130, 246, 0.5) !important;
            color: #fff !important;
        }
        
        .plyr__control svg {
            filter: drop-shadow(0 1px 2px rgba(0,0,0,0.5)) !important;
        }
        
        /* 控制栏自动隐藏 */
        .plyr.controls-auto-hide .plyr__controls {
            transition: opacity 0.3s ease, transform 0.3s ease !important;
        }
        
        .plyr.controls-hidden .plyr__controls {
            opacity: 0 !important;
            transform: translateY(100%) !important;
            pointer-events: none !important;
        }
        
        .plyr.controls-hidden .plyr__control--overlaid {
            opacity: 0 !important;
            pointer-events: none !important;
        }
        
        /* 鼠标悬停时显示 */
        .plyr.controls-hidden:hover .plyr__controls {
            opacity: 1 !important;
            transform: translateY(0) !important;
            pointer-events: auto !important;
        }
        
        .plyr.controls-hidden:hover .plyr__control--overlaid {
            opacity: 1 !important;
            pointer-events: auto !important;
        }
        
        /* 全屏按钮高亮 */
        .plyr--fullscreen-active .plyr__control[data-plyr=fullscreen] {
            background: rgba(59, 130, 246, 0.4) !important;
        }
        
        /* 倍速按钮样式 */
        .plyr__control--speed {
            display: flex !important;
            align-items: center !important;
            justify-content: center !important;
            min-width: 40px !important;
            padding: 8px 10px !important;
        }
        
        .plyr__control--speed .speed-text {
            font-size: 14px !important;
            font-weight: 600 !important;
            color: #fff !important;
            text-shadow: 0 1px 2px rgba(0,0,0,0.5) !important;
        }
        
        .plyr__control--speed:hover .speed-text {
            color: #60a5fa !important;
        }
        
        /* 倍速选择弹窗 */
        .speed-menu {
            background: rgba(30, 30, 46, 0.98) !important;
            border-radius: 8px !important;
            box-shadow: 0 4px 20px rgba(0,0,0,0.5) !important;
            padding: 8px 0 !important;
            min-width: 100px !important;
            z-index: 100 !important;
            border: 1px solid rgba(255,255,255,0.1) !important;
        }
        
        .speed-option {
            padding: 10px 20px !important;
            color: #fff !important;
            font-size: 14px !important;
            cursor: pointer !important;
            text-align: center !important;
            transition: background 0.2s !important;
        }
        
        .speed-option:hover {
            background: rgba(59, 130, 246, 0.3) !important;
        }
        
        .speed-option.active {
            color: #60a5fa !important;
            font-weight: 600 !important;
            background: rgba(59, 130, 246, 0.2) !important;
        }
        
        /* 网页全屏按钮样式 */
        .plyr__control--theater {
            display: flex !important;
            align-items: center !important;
            justify-content: center !important;
        }
        
        .plyr__control--theater svg {
            width: 20px !important;
            height: 20px !important;
        }
        
        .plyr__control--theater.plyr__control--pressed {
            background: rgba(59, 130, 246, 0.4) !important;
        }
        
        /* ==================== 网页全屏覆盖层 ==================== */
        .theater-overlay {
            position: fixed !important;
            top: 0 !important;
            left: 0 !important;
            right: 0 !important;
            bottom: 0 !important;
            z-index: 99999 !important;
            background: #000 !important;
            display: flex !important;
            align-items: center !important;
            justify-content: center !important;
        }
        
        .theater-overlay .plyr {
            width: 100% !important;
            height: 100% !important;
            max-width: 100% !important;
            max-height: 100% !important;
        }
        
        .theater-overlay .plyr video {
            width: 100% !important;
            height: 100% !important;
            object-fit: contain !important;
        }
        
        /* 退出按钮 */
        .theater-exit-btn {
            position: absolute !important;
            top: 20px !important;
            right: 20px !important;
            z-index: 100000 !important;
            background: rgba(0, 0, 0, 0.7) !important;
            color: #fff !important;
            border: 1px solid rgba(255,255,255,0.2) !important;
            border-radius: 8px !important;
            padding: 10px 20px !important;
            font-size: 14px !important;
            cursor: pointer !important;
            opacity: 0 !important;
            transition: opacity 0.3s, background 0.2s !important;
            display: flex !important;
            align-items: center !important;
            gap: 8px !important;
        }
        
        .theater-exit-btn.visible {
            opacity: 1 !important;
        }
        
        .theater-exit-btn:hover {
            background: rgba(239, 68, 68, 0.8) !important;
        }
        
        /* 浏览器全屏退出按钮 */
        .fullscreen-exit-btn {
            position: absolute !important;
            top: 20px !important;
            right: 20px !important;
            z-index: 100 !important;
            background: rgba(0, 0, 0, 0.7) !important;
            color: #fff !important;
            border: 1px solid rgba(255,255,255,0.2) !important;
            border-radius: 8px !important;
            padding: 10px 20px !important;
            font-size: 14px !important;
            cursor: pointer !important;
            opacity: 0 !important;
            transition: opacity 0.3s, background 0.2s !important;
            display: flex !important;
            align-items: center !important;
            gap: 8px !important;
        }
        
        .fullscreen-exit-btn.visible {
            opacity: 1 !important;
        }
        
        .fullscreen-exit-btn:hover {
            background: rgba(239, 68, 68, 0.8) !important;
        }
        
        /* 播放器主题色 */
        .plyr--video .plyr__control.plyr__tab-focus,
        .plyr--video .plyr__control:hover,
        .plyr--video .plyr__control[aria-expanded=true] {
            background: rgba(59, 130, 246, 0.5) !important;
        }
        
        .plyr__control--overlaid {
            background: rgba(59, 130, 246, 0.9) !important;
        }
        
        .plyr__control--overlaid:hover {
            background: rgba(59, 130, 246, 1) !important;
        }
        
        .plyr--full-ui input[type=range] {
            color: #3b82f6 !important;
        }
        
        /* 确保播放器填充容器 */
        .plyr {
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            z-index: 1;
        }
        
        .plyr__video-wrapper {
            background: #1e293b;
            height: 100%;
        }
        
        .plyr video {
            object-fit: contain;  /* 保持比例，完整显示 */
        }
        
        /* 移动端优化 */
        @media (max-width: 768px) {
            .plyr__controls {
                padding: 12px !important;
                font-size: 14px !important;
            }
            
            .plyr__control svg {
                width: 18px !important;
                height: 18px !important;
            }
            
            .plyr__progress input[type=range] {
                height: 6px !important;
            }
            
            /* 水印移动端适配 */
            .watermark-item {
                padding: 30px 40px;
                font-size: 12px;
            }
            
            .video-notice-bar {
                bottom: 50px;
                height: 24px;
            }
            
            .notice-text {
                font-size: 11px;
            }
            
            /* 触摸反馈缩小 */
            .video-touch-feedback {
                width: 60px;
                height: 60px;
                font-size: 24px;
            }
        }
        
        /* 横屏优化 */
        @media (max-height: 500px) and (orientation: landscape) {
            .course-page {
                padding-top: 0;
                height: 100vh;
                height: 100dvh;
            }
            
            .course-container {
                height: 100vh;
                height: 100dvh;
            }
            
            /* 横屏时隐藏导航栏 */
            .navbar {
                display: none !important;
            }
            
            /* 横屏时视频区域全屏 */
            .course-main {
                padding: 0;
            }
            
            /* 横屏时视频容器占满屏幕（取消 16:9 限制） */
            .video-container {
                padding-top: 0;
                position: absolute;
                top: 0;
                left: 0;
                right: 0;
                bottom: 0;
                width: 100%;
                height: 100%;
            }
            
            .video-section {
                border: none;
                border-radius: 0;
                position: relative;
                height: 100vh;
            }
            
            .video-info {
                position: absolute;
                top: 0;
                left: 0;
                right: 0;
                background: linear-gradient(to bottom, rgba(0,0,0,0.7), transparent);
                color: white;
                z-index: 15;
                padding: 12px 16px;
                opacity: 0;
                transition: opacity 0.3s;
            }
            
            .video-container:hover .video-info,
            .video-info.visible {
                opacity: 1;
            }
            
            .video-info .video-title {
                color: white;
                font-size: 14px;
            }
            
            .video-info .video-meta {
                color: rgba(255,255,255,0.7);
                font-size: 12px;
            }
            
            /* 横屏时隐藏联系老师按钮 */
            .video-info .btn-contact-teacher {
                display: none;
            }
            
            /* 横屏时菜单按钮位置调整 */
            .course-sidebar.collapsed .sidebar-collapse-btn {
                bottom: 10px;
                left: 10px;
                width: 44px;
                height: 44px;
                opacity: 0.7;
            }
            
            /* 侧边栏横屏适配 */
            .course-sidebar {
                top: 0;
                max-width: 320px;
            }
        }
        
        /* 平板优化 (768px - 1024px) */
        @media (min-width: 768px) and (max-width: 1024px) {
            .course-sidebar {
                width: 360px;
                min-width: 360px;
            }
            
            .sidebar-content {
                width: 360px;
            }
            
            .watermark-item {
                padding: 35px 50px;
                font-size: 13px;
            }
        }
        
        /* iOS 安全区域适配 */
        @supports (padding-bottom: env(safe-area-inset-bottom)) {
            .course-sidebar.collapsed .sidebar-collapse-btn {
                bottom: calc(16px + env(safe-area-inset-bottom));
                left: calc(16px + env(safe-area-inset-left));
            }
            
            .plyr__controls {
                padding-bottom: calc(10px + env(safe-area-inset-bottom)) !important;
            }
            
            @media (max-height: 500px) and (orientation: landscape) {
                .video-info {
                    padding-left: calc(16px + env(safe-area-inset-left));
                    padding-right: calc(16px + env(safe-area-inset-right));
                }
            }
        }