[MarkFL]

Okay, now I see the articles, and it appears that there is some native cms CSS interfering.

As a test, try adding the following selector to your "additional.css" template:

.showpreviewonly iframe {
    float: none !important;
    height: 100% !important;
    width: 100% !important;
    border: none !important;
    margin: 0 !important;
    outline: none !important;
}

If this works, I will add this to the product's CSS so you won't have to have these selector's in your template, nor worry about adding it to each style.