The way to customize the background of Longbox is change color as follows.

.text{
    background: black;    
color: white;
font-weight: bold;
}

The way to customize the border and background of disabled Longbox.

.text-disd{
    border: 1px solid black;    
    background: red;    

}

The way to customize the border of Longbox is change color as follows.

.text-invalid{
    border: 1px solid black;