.modal {
    position: fixed;
    top: 0;
    left: -9999px;
    width: 100%;
    bottom: 0;
    background-color: rgba(0, 0, 0, .45);   
}

.modal.open {
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 9999;
    left: 0;
}

.amoforms_iframe {
    position: absolute !important;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
}