:root {
    --primary-color: #3b82f6;
    --primary-hover: #2563eb;
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --text-main: #1e293b;
    --text-muted: #64748b;
    --border-color: #e2e8f0;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --radius: 0.75rem;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
    line-height: 1.5;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

/* Navbar */
.navbar {
    background-color: var(--card-bg);
    border-bottom: 1px solid var(--border-color);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 50;
    margin-bottom: 2rem;
}

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
    cursor: pointer;
}

/* Home View - Course Cards */
.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 2rem;
    padding-bottom: 3rem;
}

.course-card {
    background: var(--card-bg);
    border-radius: var(--radius);
    overflow: hidden;
    box-shadow: var(--shadow-sm);
    transition: transform 0.2s, box-shadow 0.2s;
    cursor: pointer;
    border: 1px solid var(--border-color);
}

.course-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
}

.course-thumbnail {
    width: 100%;
    aspect-ratio: 16/9;
    object-fit: cover;
    background-color: #e2e8f0;
}

.course-info {
    padding: 1.25rem;
}

.course-info h3 {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--text-main);
    margin-bottom: 0.5rem;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

/* Details View - Course Player */
.course-player-view {
    display: grid;
    grid-template-columns: 1fr 350px;
    gap: 2rem;
    align-items: start;
}

@media (max-width: 992px) {
    .course-player-view {
        grid-template-columns: 1fr;
    }
}

.main-content {
    background: var(--card-bg);
    border-radius: var(--radius);
    padding: 1.5rem;
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--border-color);
}

.video-container {
    position: relative;
    padding-bottom: 56.25%; /* 16:9 aspect ratio */
    height: 0;
    background: #000;
    border-radius: calc(var(--radius) - 0.25rem);
    overflow: hidden;
    margin-bottom: 1.5rem;
}

.video-container video {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

.content-info h2 {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 1rem;
}

/* Sidebar Accordion */
.sidebar {
    background: var(--card-bg);
    border-radius: var(--radius);
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--border-color);
    overflow: hidden;
}

.sidebar-header {
    padding: 1.25rem;
    border-bottom: 1px solid var(--border-color);
}

.sidebar-header h3 {
    font-size: 1.125rem;
    font-weight: 600;
}

.accordion-item {
    border-bottom: 1px solid var(--border-color);
}

.accordion-header {
    width: 100%;
    padding: 1rem 1.25rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: none;
    border: none;
    cursor: pointer;
    font-weight: 600;
    color: var(--text-main);
    text-align: left;
    transition: background-color 0.2s;
}

.accordion-header:hover {
    background-color: #f1f5f9;
}

.accordion-header::after {
    content: '▼';
    font-size: 0.75rem;
    transition: transform 0.2s;
    color: var(--text-muted);
}

#accordion-container {
    overflow-y: scroll;
    height: 65vh;
}

.accordion-item.active .accordion-header::after {
    transform: rotate(180deg);
}

.accordion-content {
    display: none;
    padding: 0.5rem 0;
    background-color: #f8fafc;
}

.accordion-item.active .accordion-content {
    display: block;
}

.lesson-item {
    padding: 0.75rem 1.25rem;
    cursor: pointer;
    font-size: 0.875rem;
    color: var(--text-muted);
    transition: all 0.2s;
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

.lesson-item:hover {
    background-color: #e2e8f0;
    color: var(--primary-color);
}

.lesson-item.active {
    background-color: #eff6ff;
    color: var(--primary-color);
    font-weight: 500;
    border-left: 3px solid var(--primary-color);
}

.download-btn {
    display: inline-flex;
    align-items: center;
    padding: 0.75rem 1.5rem;
    background-color: var(--primary-color);
    color: white;
    text-decoration: none;
    border-radius: 0.5rem;
    font-weight: 500;
    transition: background-color 0.2s;
}

.download-btn:hover {
    background-color: var(--primary-hover);
}

.no-content {
    text-align: center;
    padding: 3rem;
    color: var(--text-muted);
}