Franky,
Very sorry to be such a dunderhead, but I'm not an actual coder (as if that wasn't already clear) - I just sort of toy around on the margins and see what happens. So forgive me for my continuous follow ups:
When you say you've changed the CSS for the preview plugin, does that mean within the plugin php itself? Because it doesn't have any CSS as far as I can tell. Or did you apply the changes to the theme's style.css? Because I tried that to no avail. Is it because I don't have the "images/preview.jpg"? file do you think?
And to throw myself even further on the altar of humility, when you say that I'll find the second block of div text in source, does that mean after I've made the changes to the CSS, where ever it is those changes go?