body {
    font-family: Georgia, serif;
    background: #ffffff;
    color: #222;
    margin: 0;
}

.site-header {
    text-align: center;
    padding: 30px 20px;
    border-bottom: 1px solid #ddd;
}


.container {
    max-width: 1300px;
    margin: 40px auto;
    padding: 0 20px;
}

.lesson-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 20px;
}

.lesson-card {
    padding: 20px;
    border: 1px solid #ddd;
    transition: 0.2s ease;
}

.lesson-card:hover {
    border-color: #333;
}

.lesson-title {
    font-size: 18px;
    font-weight: bold;
}

.lesson-layout {
    display: flex;
    gap: 40px;
}

.lesson-content {
    flex: 3;
}

.lesson-sidebar {
    flex: 1;
    border-left: 1px solid #ddd;
    padding-left: 20px;
}

.sidebar-item {
    margin-bottom: 12px;
}


.yt-layout {
    display: grid;
    grid-template-columns: 3fr 1.2fr;
    gap: 40px;
}

.yt-main {
    min-width: 0;
}

.yt-sidebar {
    border-left: 1px solid #ddd;
    padding-left: 20px;
    max-height: 85vh;
    overflow-y: auto;
}

.yt-thumb {
    padding: 10px;
    margin-bottom: 10px;
    border-bottom: 1px solid #eee;
}

.yt-thumb a {
    text-decoration: none;
    color: #333;
}

.yt-thumb:hover {
    background: #f5f5f5;
}

.active-thumb {
    background: #e9ecef;
    font-weight: bold;
}

.lesson-body img {
    max-width: 100%;
    height: auto;
}

.lesson-body p {
    line-height: 1.7;
}

.lesson-body h1,
.lesson-body h2,
.lesson-body h3 {
    margin-top: 30px;
}

.site-footer {
    text-align: center;
    padding: 30px;
    border-top: 1px solid #ddd;
    margin-top: 60px;
}
@media (max-width: 900px) {
    .yt-layout {
        grid-template-columns: 1fr;
    }

    .yt-sidebar {
        border-left: none;
        padding-left: 0;
        margin-top: 40px;
    }
}