Add the following css to the My Custom CSS.
@media screen and (max-width: 480px) {
.multi-office-select .office-box .btn-office {
min-width: 100px;
font-size: 12px;
padding: 20px 0px;
}
.multi-office-select .office-box .btn-office .fa {
font-size: 32px;
}
}
Example – Where to place the code: