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

body {
    font-family: 'Segoe UI', system-ui, sans-serif;
    display: flex;
    background: #f5f7fa;
    color: #1e293b;
    line-height: 1.5;
}

.sidebar {
    width: 300px;
    background: #ffffff;
    border-right: 1px solid #e2e8f0;
    height: 100vh;
    overflow-y: auto;
    position: fixed;
    top: 0;
    left: 0;
    transform: translateX(-100%);
    transition: transform 0.3s ease;
    z-index: 100;
    padding: 1.5rem 1rem;
    box-shadow: 2px 0 8px rgba(0,0,0,0.05);
}

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

.sidebar-header {
    margin-bottom: 2rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid #e2e8f0;
}

.sidebar-header h2 {
    font-size: 1.3rem;
    font-weight: 600;
    margin-bottom: 0.2rem;
}

.subtitle {
    font-size: 0.8rem;
    color: #64748b;
    margin-bottom: 1rem;
}

.progress-container {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.progress-bar {
    flex: 1;
    height: 6px;
    background: #e2e8f0;
    border-radius: 3px;
    overflow: hidden;
}

.progress-bar::after {
    content: '';
    display: block;
    height: 100%;
    width: var(--progress, 0%);
    background: #3b82f6;
    transition: width 0.3s ease;
}

.progress-text {
    font-size: 0.8rem;
    font-weight: 600;
    color: #3b82f6;
}

.session-nav {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: 0.3rem;
}

.session-nav li {
    padding: 0.6rem 0.8rem;
    border-radius: 6px;
    cursor: pointer;
    transition: background 0.2s;
    font-size: 0.9rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.session-nav li:hover {
    background: #f1f5f9;
}

.session-nav li.active {
    background: #eef2ff;
    font-weight: 600;
    color: #2563eb;
}

.session-nav li .check-icon {
    opacity: 0;
    color: #10b981;
    font-size: 0.8rem;
}

.session-nav li.completed .check-icon {
    opacity: 1;
}

.sidebar-toggle {
    position: fixed;
    top: 1rem;
    left: 1rem;
    background: #ffffff;
    border: 1px solid #e2e8f0;
    border-radius: 6px;
    padding: 0.5rem 0.8rem;
    font-size: 1.2rem;
    cursor: pointer;
    z-index: 200;
    box-shadow: 0 2px 6px rgba(0,0,0,0.05);
}

.main-content {
    flex: 1;
    margin-left: 0;
    transition: margin-left 0.3s ease;
    padding: 2rem;
    max-width: 900px;
    width: 100%;
    margin: 0 auto;
}

.sidebar.open ~ .main-content {
    margin-left: 300px;
}

.overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0,0,0,0.3);
    z-index: 90;
    display: none;
}

.overlay.active {
    display: block;
}

.session-page {
    display: none;
}

.session-page.active {
    display: block;
    animation: fadeIn 0.3s ease;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

.session-page h1 {
    font-size: 2rem;
    margin-bottom: 0.5rem;
    color: #0f172a;
}

.session-meta {
    color: #64748b;
    font-size: 0.9rem;
    margin-bottom: 1.5rem;
}

.session-content {
    background: #ffffff;
    border-radius: 12px;
    padding: 2rem;
    box-shadow: 0 4px 12px rgba(0,0,0,0.03);
    margin-bottom: 2rem;
}

.session-content h2 {
    font-size: 1.3rem;
    margin-top: 1.8rem;
    margin-bottom: 0.8rem;
    color: #1e293b;
    border-bottom: 1px solid #e2e8f0;
    padding-bottom: 0.3rem;
}

.session-content ul {
    margin-left: 1.2rem;
    margin-bottom: 1rem;
}

.session-content li {
    margin-bottom: 0.4rem;
}

.review-block {
    background: #f0fdf4;
    border-left: 4px solid #10b981;
    padding: 1.5rem;
    border-radius: 8px;
    margin-top: 1.5rem;
}

.review-block h3 {
    color: #065f46;
    margin-bottom: 0.8rem;
    display: flex;
    align-items: center;
    gap: 0.4rem;
}

.session-check {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-top: 1.5rem;
    font-weight: 500;
    cursor: pointer;
}

.session-check input {
    width: 1.2rem;
    height: 1.2rem;
}

.session-nav li {
    font-size: 0.85rem;
}

@media (min-width: 768px) {
    .sidebar {
        transform: translateX(0);
    }
    .sidebar-toggle {
        display: none;
    }
    .main-content {
        margin-left: 300px;
    }
}