.acf-image-grid {
    width: 100%;
    max-width: 100%;
}

.acf-image-grid__item + .acf-image-grid__item {
    margin-top: 1em;
}

.acf-image-grid__img {
    display: block;
    width: 100%;
    height: auto;
    max-width: 100%;
}