/* General */
body {
    font-family: Arial, sans-serif;
    margin: 0;
    background-color: #f5f5f5;
}

/* Header */
header {
    background-color: #2c3e50;
    color: white;
    padding: 15px;
    text-align: center;
}

/* Navigation */
nav {
    background-color: #34495e;
    padding: 10px;
    text-align: center;
}

nav a {
    color: white;
    margin: 0 15px;
    text-decoration: none;
    font-weight: bold;
}

nav a:hover {
    text-decoration: underline;
}

/* Main Layout */
.container {
    display: flex;
}

/* Sidebar */
.sidebar {
    width: 200px;
    background: #ecf0f1;
    padding: 15px;
}

.sidebar h3 {
    margin-top: 0;
}

.sidebar a {
    display: block;
    padding: 10px;
    text-decoration: none;
    color: black;
    margin-bottom: 5px;
    cursor: pointer;
    border-radius: 5px;
}

.sidebar a:hover {
    background: #bdc3c7;
}

/* Content Area */
.content {
    flex: 1;
    padding: 20px;
    background: white;
}

/* Subject Tabs */
.tabs {
    margin-bottom: 15px;
}

.tabs button {
    padding: 10px 15px;
    margin-right: 10px;
    cursor: pointer;
    border: none;
    background: #34495e;
    color: white;
    border-radius: 5px;
}

.tabs button:hover {
    background: #2c3e50;
}

.tab-content {
    display: none;
    margin-top: 15px;
}

/* Chapter Dropdown */
.chapter {
    margin-top: 10px;
}

.chapter button {
    width: 100%;
    padding: 12px;
    border: none;
    background: #dfe6e9;
    cursor: pointer;
    text-align: left;
    font-weight: bold;
    border-radius: 5px;
}

.chapter button:hover {
    background: #ced6e0;
}

.chapter-content {
    display: none;
    padding: 15px;
    background: #f9f9f9;
    border-left: 4px solid #34495e;
    margin-top: 5px;
}

/* ---------- MULTI VIDEO LAYOUT ---------- */

.video-row {
    display: flex;
    gap: 15px;
    flex-wrap: wrap;
    margin-bottom: 15px;
}

.video-row iframe {
    flex: 1;
    min-width: 300px;
    height: 250px;
    border-radius: 6px;
}

/* Single Video */
iframe {
    width: 100%;
    height: 315px;
    margin-top: 10px;
    border-radius: 6px;
}

/* Links */
.chapter-content a {
    display: inline-block;
    margin-top: 8px;
    color: #2980b9;
    text-decoration: none;
    font-weight: bold;
}

.chapter-content a:hover {
    text-decoration: underline;
}

/* Footer */
footer {
    background-color: #2c3e50;
    color: white;
    text-align: center;
    padding: 15px;
    margin-top: 20px;
}

/* ---------- MOBILE RESPONSIVE ---------- */

@media (max-width: 768px) {

.container {
    flex-direction: column;
}

.sidebar {
    width: 100%;
}

.video-row {
    flex-direction: column;
}

.video-row iframe {
    width: 100%;
}

}