:root {
    --primary-color: #0d6efd;
    --primary-dark: #0a58ca;
    --bg-light: #f8f9fa;
    --sidebar-width: 360px;
}

* {
    font-family: 'Inter', sans-serif;
}

a {
    text-decoration: none;
}

body {
    margin: 0;
    background-color: var(--bg-light);
}

/* Main Layout */
.learning-container {
    height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header */
.learning-header {
    background: var(--primary-color);
    color: white;
    padding: 0.75rem 1.5rem;
    flex-shrink: 0;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.learning-header h6 {
    max-width: 400px;
}

/* Body Layout */
.learning-body {
    flex: 1;
    display: flex;
    overflow: hidden;
}

/* Main Content Area */
.lesson-content {
    flex: 1;
    padding: 2rem;
    overflow-y: auto;
    background: white;
}

.content-card {
    max-width: 900px;
    margin: 0 auto;
}

/* Video Container */
.video-container {
    position: relative;
    padding-bottom: 56.25%; /* 16:9 ratio */
    height: 0;
    overflow: hidden;
    background: #000;
    border-radius: 12px;
    box-shadow: 0 4px 12px rgba(0,0,0,0.15);
}

iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: none;
}

/* Text Content */
.text-content {
    background: #f8f9fa;
    border-radius: 12px;
    padding: 2rem;
    line-height: 1.8;
    font-size: 1.05rem;
}

.text-content h1, .text-content h2, .text-content h3 {
    color: var(--primary-color);
    margin-top: 1.5rem;
    margin-bottom: 1rem;
}

.text-content p {
    margin-bottom: 1rem;
}

.text-content code {
    background: #e9ecef;
    padding: 0.2rem 0.4rem;
    border-radius: 4px;
}

.text-content pre {
    background: #1e1e1e;
    color: #d4d4d4;
    padding: 1rem;
    border-radius: 8px;
    overflow-x: auto;
}

/* Lesson Info Card */
.lesson-info-card {
    background: #f8f9fa;
    border-radius: 12px;
    padding: 1.5rem;
    margin-top: 1.5rem;
}

/* Navigation Controls */
.lesson-controls {
    background: #fff;
    padding: 1.5rem 0;
    border-top: 1px solid #eee;
    margin-top: 2rem;
}

/* Sidebar */
.course-sidebar {
    width: var(--sidebar-width);
    background: #ffffff;
    border-left: 1px solid #e0e0e0;
    overflow-y: auto;
    display: flex;
    flex-direction: column;
}

.sidebar-header {
    padding: 1rem 1.25rem;
    border-bottom: 1px solid #eee;
    background: #f8f9fa;
    position: sticky;
    top: 0;
    z-index: 10;
}

.chapter-header {
    background: #e9ecef;
    color: #495057;
    padding: 0.75rem 1rem;
    font-weight: 600;
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    border-bottom: 1px solid #dee2e6;
    position: sticky;
    top: 60px;
    z-index: 5;
}

.lesson-item {
    border-bottom: 1px solid #f0f0f0;
    padding: 0.875rem 1rem;
    cursor: pointer;
    transition: all 0.2s;
    display: flex;
    align-items: center;
    text-decoration: none;
    color: inherit;
}

.lesson-item:hover {
    background-color: #f5f7ff;
}

.lesson-item.active {
    background-color: #e7f1ff;
    border-left: 4px solid var(--primary-color);
}

.lesson-item.active .lesson-title {
    color: var(--primary-color);
    font-weight: 600;
}

.lesson-icon {
    width: 32px;
    height: 32px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 50%;
    margin-right: 0.75rem;
    font-size: 0.9rem;
}

.lesson-icon.video {
    background: #e3f2fd;
    color: #1976d2;
}

.lesson-icon.text {
    background: #fff3e0;
    color: #f57c00;
}

.lesson-icon.quiz {
    background: #f3e5f5;
    color: #7b1fa2;
}

.lesson-icon.assignment {
    background: #e8f5e9;
    color: #388e3c;
}

.lesson-title {
    font-size: 0.9rem;
    font-weight: 500;
    color: #333;
    margin-bottom: 2px;
}

.lesson-meta {
    font-size: 0.75rem;
    color: #888;
}

.preview-badge {
    font-size: 0.65rem;
    padding: 0.15rem 0.4rem;
    background: #17a2b8;
    color: white;
    border-radius: 3px;
    margin-left: 0.5rem;
}

/* Mobile Responsive */
@media (max-width: 992px) {
    .course-sidebar {
        position: fixed;
        right: -360px;
        top: 0;
        height: 100vh;
        z-index: 1050;
        transition: right 0.3s ease;
        box-shadow: -4px 0 10px rgba(0,0,0,0.1);
    }

    .course-sidebar.show {
        right: 0;
    }

    .sidebar-backdrop {
        display: none;
        position: fixed;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        background: rgba(0,0,0,0.5);
        z-index: 1040;
    }

    .sidebar-backdrop.show {
        display: block;
    }
}

/* No content styles */
.no-content {
    text-align: center;
    padding: 3rem;
    color: #6c757d;
}

.no-content i {
    font-size: 4rem;
    margin-bottom: 1rem;
    opacity: 0.5;
}