.mainCol .article-top-content img {
    margin: 0 auto;
}
.wp-block-acf-top-image.acf-block-preview img {
    height: auto;
    max-width: 100%;
    width: 100%;
}
@media only screen and (min-width: 768px)  {
    .wp-block-acf-top-image.acf-block-preview img {
        max-width: 995px;
    }        
}