.bx-authform button.btn[name="regform_show_button"] {
    display:none;
}

@media (max-width: 991px) {
    .bx-authform {
        margin: 0 auto 25px;
    }
    .bx-authform button.btn[name="regform_show_button"] {
        display:inline-block;
        margin-top: 25px;
    }
    .bx-authform .btn-lg {
        padding: 0.5rem 1rem;
        font-size: 1.6rem;
        line-height: 2;
        border-radius: 0.7rem;
        width: 100%;
    }
}