/* Course Layout */
.course-container {
    display: flex;
    flex: 1;
    overflow: hidden;
    background-color: var(--bg-body);
}

/* Chapter Sidebar (Left) */
.chapter-sidebar {
    width: 300px;
    background-color: white;
    border-right: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.chapter-header {
    padding: 1.5rem;
    border-bottom: 1px solid var(--border);
    background-color: #f8fafc;
}

.chapter-header h3 {
    font-size: 1rem;
    color: var(--secondary);
    margin-bottom: 0.25rem;
}

.chapter-list {
    flex: 1;
    overflow-y: auto;
    padding: 0;
}

.chapter-item {
    padding: 1rem 1.5rem;
    border-bottom: 1px solid var(--border);
    cursor: pointer;
    transition: all 0.2s;
    display: flex;
    align-items: center;
    gap: 10px;
}

.chapter-item:hover {
    background-color: #f1f5f9;
}

.chapter-item.active {
    background-color: #e0e7ff;
    border-left: 4px solid var(--primary);
}

.chapter-number {
    width: 24px;
    height: 24px;
    background-color: #e2e8f0;
    color: var(--text-light);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.75rem;
    font-weight: 600;
}

.chapter-item.active .chapter-number {
    background-color: var(--primary);
    color: white;
}

.chapter-title {
    font-size: 0.9rem;
    font-weight: 500;
    color: var(--text-main);
}

/* Content Display (Right) */
.content-display {
    flex: 1;
    overflow-y: auto;
    padding: 3rem 4rem;
    background-color: white;
    transition: opacity 0.3s ease;
    scroll-behavior: smooth;
}

.empty-state {
    height: 100%;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    color: var(--text-light);
    opacity: 0.5;
}

/* Article Styling */
.lesson-article {
    max-width: 800px;
    margin: 0 auto;
    animation: fadeIn 0.3s ease-out;
}

.article-header {
    margin-bottom: 2.5rem;
    border-bottom: 1px solid var(--border);
    padding-bottom: 1.5rem;
}

.article-title {
    font-size: 2rem;
    color: var(--secondary);
    margin-bottom: 0.5rem;
    line-height: 1.2;
}

.article-meta {
    font-size: 0.9rem;
    color: var(--text-light);
    display: flex;
    align-items: center;
    gap: 10px;
}

.article-body {
    line-height: 1.8;
    color: var(--text-main);
    font-size: 1.05rem;
}

.article-body h2 {
    font-size: 1.5rem;
    margin-top: 2.5rem;
    margin-bottom: 1rem;
    color: var(--secondary);
}

.article-body h3 {
    font-size: 1.25rem;
    margin-top: 2rem;
    margin-bottom: 0.75rem;
    color: var(--text-main);
}

.article-body p {
    margin-bottom: 1.5rem;
}

.article-body ul,
.article-body ol {
    margin-bottom: 1.5rem;
    padding-left: 1.5rem;
}

.article-body li {
    margin-bottom: 0.5rem;
}

.article-body blockquote {
    border-left: 4px solid var(--primary);
    padding-left: 1rem;
    margin: 1.5rem 0;
    color: var(--text-light);
    font-style: italic;
    background-color: #f8fafc;
    padding: 1rem;
    border-radius: 0 8px 8px 0;
}

.tip-box {
    background-color: #ecfdf5;
    border: 1px solid #a7f3d0;
    border-radius: 8px;
    padding: 1.5rem;
    margin: 2rem 0;
    color: #064e3b;
    display: flex;
    gap: 1rem;
    align-items: flex-start;
}

.tip-box i {
    font-size: 1.5rem;
    color: #059669;
}