:root {
    --primary-color: #FFD700;
    --secondary-color: #000000;
    --accent-color: #1a1a1a;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #f5f5f5;
}

.navbar-brand img {
    border-radius: 50%;
}

.card {
    border: none;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    margin-bottom: 20px;
}

.card-header {
    background: linear-gradient(135deg, var(--secondary-color) 0%, var(--accent-color) 100%);
    color: var(--primary-color);
    font-weight: bold;
}

.btn-primary {
    background-color: var(--secondary-color);
    border-color: var(--secondary-color);
    color: var(--primary-color);
}

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

.btn-outline-primary {
    border-color: var(--secondary-color);
    color: var(--secondary-color);
}

.btn-outline-primary:hover {
    background-color: var(--secondary-color);
    border-color: var(--secondary-color);
    color: var(--primary-color);
}

.badge {
    padding: 0.35em 0.65em;
}

.table thead {
    background-color: var(--secondary-color);
    color: var(--primary-color);
}

.sidebar {
    min-height: calc(100vh - 56px);
    background-color: #fff;
    box-shadow: 2px 0 5px rgba(0,0,0,0.1);
}

.sidebar .nav-link {
    color: #333;
    padding: 12px 20px;
    border-left: 3px solid transparent;
}

.sidebar .nav-link:hover,
.sidebar .nav-link.active {
    background-color: #f8f9fa;
    border-left-color: var(--secondary-color);
    color: var(--secondary-color);
}

.stats-card {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    border-radius: 10px;
    padding: 20px;
    margin-bottom: 20px;
}

.stats-card h3 {
    font-size: 2.5rem;
    font-weight: bold;
    margin: 0;
}

.stats-card p {
    margin: 5px 0 0 0;
    opacity: 0.9;
}

.alert {
    border-radius: 8px;
}

.form-control:focus,
.form-select:focus {
    border-color: var(--secondary-color);
    box-shadow: 0 0 0 0.2rem rgba(0, 0, 0, 0.25);
}

.message-item {
    border-left: 4px solid var(--secondary-color);
    padding: 15px;
    margin-bottom: 15px;
    background-color: #fff;
    border-radius: 5px;
}

.message-item.unread {
    background-color: #f8f9fa;
    border-left-color: var(--primary-color);
}

.virtual-class-card {
    border: 2px solid var(--primary-color);
    border-radius: 10px;
    padding: 20px;
    margin-bottom: 20px;
    background: linear-gradient(135deg, #fff 0%, #f8f9fa 100%);
}

.assignment-card,
.test-card {
    transition: transform 0.2s;
}

.assignment-card:hover,
.test-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 4px 15px rgba(0,0,0,0.2);
}