/* --- 1. 全局样式重置 --- */
* { margin: 0; padding: 0; box-sizing: border-box; }
body { font-family: "Microsoft YaHei", Arial, sans-serif; background-color: #f9f9f9; color: #333; }
a { text-decoration: none; color: inherit; }
ul { list-style: none; }

/* --- 2. 布局容器 (模仿您官网的结构) --- */
.container {
    display: flex;
    max-width: 1400px;
    margin: 0 auto;
    min-height: 100vh;
}

/* --- 3. 左侧导航栏 (还原您截图中的蓝色菜单) --- */
.sidebar {
    width: 220px;
    background-color: #0056b3; /* 您官网的深蓝色 */
    color: #fff;
    flex-shrink: 0;
    display: flex;
    flex-direction: column;
}

.logo-area {
    height: 100px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 24px;
    font-weight: bold;
    border-bottom: 1px solid rgba(255,255,255,0.1);
    background: #004494;
}

.logo-area img {
    max-height: 80%; /* 控制Logo大小 */
}

.nav-menu {
    padding: 20px 0;
}
.nav-item {
    padding: 15px 20px;
    cursor: pointer;
    transition: background 0.3s;
    border-left: 4px solid transparent;
}
.nav-item:hover, .nav-item.active {
    background-color: rgba(255,255,255,0.1);
    border-left-color: #fff;
}

/* --- 4. 右侧内容区 (参考 Up-Concepts 的视频风格) --- */
.main-content {
    flex: 1;
    padding: 40px;
    background-color: #fff;
}

/* 顶部面包屑 */
.breadcrumb {
    font-size: 14px;
    color: #666;
    margin-bottom: 30px;
    border-bottom: 1px solid #eee;
    padding-bottom: 15px;
}
.breadcrumb span { color: #0056b3; font-weight: bold; }

/* 页面大标题 */
.page-title {
    font-size: 32px;
    margin-bottom: 40px;
    color: #222;
    position: relative;
    padding-left: 15px;
}
.page-title::before {
    content: '';
    position: absolute;
    left: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 5px;
    height: 30px;
    background-color: #0056b3;
}

/* --- 5. 视频网格布局 (核心部分) --- */
.video-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 30px;
}

/* 视频卡片样式 */
.video-card {
    position: relative;
    background: #000;
    border-radius: 4px;
    overflow: hidden;
    cursor: pointer;
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
    transition: transform 0.3s ease;
    aspect-ratio: 16/9; /* 保持视频比例 */
}

.video-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 25px rgba(0,0,0,0.2);
}

/* 视频封面/视频本身 */
.video-thumbnail {
    width: 100%;
    height: 100%;
    object-fit: cover;
    opacity: 0.9;
    transition: opacity 0.3s;
}

.video-card:hover .video-thumbnail {
    opacity: 0.6; /* 悬停变暗 */
}

/* 播放按钮图标 (CSS绘制) */
.play-icon {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 60px;
    height: 60px;
    background: rgba(0, 86, 179, 0.8);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0; /* 默认隐藏 */
    transition: opacity 0.3s;
}

.video-card:hover .play-icon {
    opacity: 1; /* 悬停显示 */
}

.play-icon::after {
    content: '';
    display: block;
    width: 0;
    height: 0;
    border-left: 15px solid #fff;
    border-top: 10px solid transparent;
    border-bottom: 10px solid transparent;
    margin-left: 5px; /* 视觉修正 */
}

/* 视频信息遮罩层 */
.video-info {
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    padding: 20px;
    background: linear-gradient(to top, rgba(0,0,0,0.8), transparent);
    color: #fff;
    transform: translateY(100%); /* 默认隐藏在底部 */
    transition: transform 0.3s;
}

.video-card:hover .video-info {
    transform: translateY(0); /* 悬停滑上来 */
}

.video-info h3 {
    font-size: 18px;
    margin-bottom: 5px;
}
.video-info p {
    font-size: 12px;
    color: #ddd;
}

/* 标签样式 (模仿您截图中的蓝色标签) */
.tag {
    position: absolute;
    top: 15px;
    right: 15px;
    background: #0056b3;
    color: #fff;
    padding: 4px 10px;
    font-size: 12px;
    border-radius: 2px;
    z-index: 2;
}