.aocp-client-entry .aocp-entry__login {
    width: 100%;
    max-width: 540px;
}

@media (max-width: 540px) {
    .aocp-client-entry .aocp-entry__form-row { flex-direction: column; }
    .aocp-client-entry .aocp-entry__input { flex-basis: auto; }
}