In the template file, just select the part of xml ranging from the start of the file up to the line above the stylesheet definition and copy it. This we can call the “header”. Where the Stylesheets start, there’s the content of your page. Then in the index.xml that comes from your Domain.sites, paste it in so it replaces the part up to the line avove the stylesheet. That part is done with. Now we move the end of the file....
NOTE: There’s an entry here called BLMetaDataBrowserBackgroundColor. Guess what that does if you replace it with a full color setting in there? Indeed, it does change the backgroundcolor. I’ve tried to find out if there was an option to get a background-picture. No luck. Whatever I tried, it didn’t give the required result. Digging into the code of iWeb itself, there wasn’t a recognisable chunk that gave a hint on how to achieve it either.