:root {
    --primary-color: #2b7af0;
    --primary-hover: #1e5eba;
    --bg-color: #f4f7f6;
    --sidebar-bg: #ffffff;
    --text-main: #333333;
    --text-muted: #6b7280;
    --border-color: #e5e7eb;
    --card-bg: #ffffff;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --radius: 8px;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
}

.app-container {
    display: flex;
    height: 100vh;
    overflow: hidden;
}

/* Sidebar */
.sidebar {
    width: 280px;
    background-color: var(--sidebar-bg);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    z-index: 100;
    transition: transform 0.3s ease;
}

.sidebar-header {
    padding: 20px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.logo {
    max-width: 180px;
    height: auto;
}

.close-sidebar-btn {
    display: none;
    background: none;
    border: none;
    font-size: 24px;
    cursor: pointer;
    color: var(--text-muted);
}

.sidebar-nav {
    flex: 1;
    overflow-y: auto;
    padding: 20px 0;
}

.module-btn {
    width: 100%;
    text-align: left;
    padding: 12px 20px;
    background: none;
    border: none;
    font-size: 15px;
    font-weight: 500;
    color: var(--text-main);
    cursor: pointer;
    transition: all 0.2s;
    border-left: 3px solid transparent;
}

.module-btn:hover {
    background-color: var(--bg-color);
}

.module-btn.active {
    background-color: rgba(43, 122, 240, 0.05);
    color: var(--primary-color);
    border-left-color: var(--primary-color);
}

/* Main Content */
.main-content {
    flex: 1;
    display: flex;
    flex-direction: column;
    overflow-y: auto;
}

.topbar {
    height: 70px;
    background-color: var(--card-bg);
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    padding: 0 30px;
    box-shadow: var(--shadow-sm);
}

.menu-btn {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    margin-right: 15px;
    color: var(--text-main);
}

.page-title {
    font-size: 18px;
    font-weight: 600;
}

.content-area {
    padding: 30px;
    max-width: 1000px;
    margin: 0 auto;
    width: 100%;
}

/* Video Player */
.video-container {
    width: 100%;
    aspect-ratio: 16 / 9;
    background-color: #000;
    border-radius: var(--radius);
    overflow: hidden;
    margin-bottom: 20px;
    box-shadow: var(--shadow-md);
    display: flex;
    align-items: center;
    justify-content: center;
}

.video-container iframe,
.video-container video {
    width: 100%;
    height: 100%;
    border: none;
}

.video-placeholder {
    color: #fff;
    font-size: 16px;
    opacity: 0.7;
}

.lesson-details {
    background-color: var(--card-bg);
    padding: 24px;
    border-radius: var(--radius);
    box-shadow: var(--shadow-sm);
    margin-bottom: 30px;
}

.lesson-details h2 {
    font-size: 22px;
    margin-bottom: 10px;
}

.lesson-details p {
    color: var(--text-muted);
    line-height: 1.6;
}

/* Lessons List */
.lessons-list-container h3 {
    font-size: 18px;
    margin-bottom: 15px;
    padding-bottom: 10px;
    border-bottom: 1px solid var(--border-color);
}

/* Navigation Buttons */
.lesson-navigation {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
}

.btn-nav {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 10px 16px;
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    color: var(--text-main);
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s;
}

.btn-nav:hover:not(:disabled) {
    background-color: var(--bg-color);
    border-color: var(--primary-color);
    color: var(--primary-color);
}

.btn-nav:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Sidebar Lessons */
.sidebar-lessons {
    padding-left: 10px;
    margin-bottom: 10px;
    border-left: 2px solid var(--border-color);
    margin-left: 20px;
    margin-top: 5px;
}

.sidebar-lesson-btn {
    width: 100%;
    text-align: left;
    padding: 8px 10px;
    background: none;
    border: none;
    font-size: 13px;
    color: var(--text-muted);
    cursor: pointer;
    border-radius: 4px;
    margin-bottom: 2px;
    display: flex;
    align-items: center;
    gap: 8px;
    transition: background-color 0.2s;
}

.sidebar-lesson-btn:hover {
    background-color: rgba(43, 122, 240, 0.05);
}

.sidebar-lesson-btn.active {
    color: var(--primary-color);
    font-weight: 600;
    background-color: rgba(43, 122, 240, 0.05);
}

.sidebar-lesson-btn .play-icon {
    width: 14px;
    height: 14px;
    flex-shrink: 0;
}

.lessons-list {
    display: grid;
    gap: 15px;
}

.lesson-card {
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 15px 20px;
    cursor: pointer;
    transition: all 0.2s;
    display: flex;
    flex-direction: column;
}

.lesson-card:hover {
    box-shadow: var(--shadow-md);
    border-color: var(--primary-color);
    transform: translateY(-2px);
}

.lesson-card.active {
    border-color: var(--primary-color);
    background-color: rgba(43, 122, 240, 0.02);
}

.lesson-card-title {
    font-weight: 600;
    margin-bottom: 5px;
    color: var(--text-main);
}

.lesson-card-desc {
    font-size: 13px;
    color: var(--text-muted);
}

.sidebar-overlay {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(0, 0, 0, 0.5);
    z-index: 90;
}

/* Responsive */
@media (max-width: 768px) {
    .sidebar {
        position: fixed;
        top: 0;
        bottom: 0;
        left: 0;
        transform: translateX(-100%);
    }

    .sidebar.open {
        transform: translateX(0);
    }

    .close-sidebar-btn {
        display: block;
    }

    .menu-btn {
        display: block;
    }

    .sidebar-overlay.active {
        display: block;
    }

    .content-area {
        padding: 20px;
    }
}