.modal-dialog {
    max-width: 100%;
}

@media (min-width: 576px) {
    .modal-dialog {
        max-width: 90%;
    }
}

@media (min-width: 768px) {
    .modal-dialog {
        max-width: 80%;
    }
}

@media (min-width: 992px) {
    .modal-dialog {
        max-width: 70%;
    }
}

@media (min-width: 1200px) {
    .modal-dialog {
        max-width: 60%;
    }
}

.modal-body .form-group {
    width: 100%;
}