@media (min-width: 576px) {
    .modal-dialog {
        margin: 1.75rem auto;
        max-width: 500px!important;
    }
}

@media (max-device-width: 480px) {
    .modal-dialog {
        margin: 1.75rem auto;
        max-width: 400px;
    }
}
@media (min-width: 960px) {
    .modal-dialog {
        margin: 1.75rem auto;
        max-width: 900px!important;
    }
}