:root {
            --primary-color: #3498db;
            --secondary-color: #2c3e50;
            --accent-color: #e74c3c;
            --light-gray: #f8f9fa;
            --dark-gray: #343a40;
        }
        
        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            background-color: #f5f5f5;
            margin: 0;
            padding: 0;
        }
        
        .sidebar {
            background-color: var(--secondary-color);
            color: white;
            height: 100vh;
            position: fixed;
            padding-top: 20px;
            width: 250px;
        }
        
        .sidebar .nav-link {
            color: rgba(255, 255, 255, 0.8);
            margin-bottom: 5px;
            border-radius: 5px;
            padding: 10px 15px;
        }
        
        .sidebar .nav-link:hover, .sidebar .nav-link.active {
            background-color: var(--primary-color);
            color: white;
        }
        
        .sidebar .nav-link i {
            margin-right: 10px;
        }
        
        .main-content {
            margin-left: 250px;
            padding: 20px;
        }
        
        .dashboard-card {
            border-radius: 10px;
            box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
            transition: transform 0.3s;
            margin-bottom: 20px;
        }
        
        .dashboard-card:hover {
            transform: translateY(-5px);
        }
        
        .card-icon {
            font-size: 2rem;
            margin-bottom: 15px;
        }
        
        /* Invoice form styling */
        .invoice-item-row td {
            vertical-align: middle;
        }
        
        .invoice-item-row .form-control {
            min-width: 100px;
        }