.example4 select:required {
    border-left: 4px solid #e74c3c;
}

.example4 select:optional {
    border-left: 4px solid #27ae60;
}

.example4 select {
    width: 100%;
    padding: 10px;
    margin-bottom: 15px;
    border: 1px solid #ddd;
    border-radius: 4px;
}

.example4 label {
    display: block;
    margin-bottom: 5px;
    font-weight: bold;
}