:root {
    --sidebar-width: 250px;
}

body {
    background-color: #f5f6fa;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

.sidebar {
    width: var(--sidebar-width);
    min-height: 100vh;
    position: sticky;
    top: 0;
    flex-shrink: 0;
    display: flex;
    flex-direction: column;
    transition: width 0.3s ease;
    z-index: 1000;
}

.sidebar .nav-link {
    padding: 0.7rem 1rem;
    border-radius: 0;
    transition: all 0.2s;
}

.sidebar .nav-link:hover {
    background-color: rgba(255, 255, 255, 0.1);
}

.sidebar .nav-link.active {
    background-color: rgba(13, 110, 253, 0.2);
    border-left: 3px solid #0d6efd;
}

.main-content {
    min-height: 100vh;
}

.card {
    border: none;
    border-radius: 8px;
}

.card-header {
    border-bottom: 1px solid rgba(0,0,0,.05);
}

.bg-gradient-primary {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
}

.lesson-content {
    line-height: 1.8;
}

.lesson-content h1, .lesson-content h2, .lesson-content h3 {
    margin-top: 1.5rem;
    margin-bottom: 0.5rem;
}

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

.lesson-content img {
    max-width: 100%;
    height: auto;
}

.lesson-content ul, .lesson-content ol {
    margin-bottom: 1rem;
    padding-left: 2rem;
}

.pagination .page-link {
    border: none;
    margin: 0 2px;
    border-radius: 4px !important;
}

.table th {
    font-weight: 600;
    font-size: 0.85rem;
}

.progress {
    border-radius: 10px;
}

@media (max-width: 991px) {
    .sidebar {
        width: 60px;
        overflow: hidden;
    }
    .sidebar .nav-link span {
        display: none;
    }
    .sidebar-header small {
        display: none;
    }
    .sidebar-header span {
        display: none;
    }
    .sidebar-footer span {
        display: none;
    }
}

@media (max-width: 576px) {
    .sidebar {
        width: 0;
        overflow: hidden;
        position: fixed;
        left: 0;
        top: 0;
    }
    .sidebar.show {
        width: var(--sidebar-width);
    }
}

.alert {
    border: none;
    border-radius: 8px;
}

.btn {
    border-radius: 6px;
}

.form-control, .form-select {
    border-radius: 6px;
}