I have no magic answer for this one. When you say you have "looked and looked" that doesn't really make sense unless you are thinking that CSS is a simple set of key value switches to turn things on and off but it isn't like that at all, the selectors are usually more complex involving multiple classes to select things nested in places where they are expected to be. Artisteer has some conventions for their class names where side columns are usually like art-block and center content is like art-post and there are lots of variants and other nested classes used to style things.
Artisteer does not generate any CSS that would be for styling those extra content regions, you would have to make up your own. While you might be able to copy some style rules from the existing artisteer CSS the selectors they use would not be appropriate. The classes they use for column layouts is different than traditional mojoportal skins but is mentioned at the bottom of the article How The Main Content Layout Works, but those classes only are for the column layout as far as using them elsewhere it would not make sense.
So basically I'm saying there isn't something to look for as far as magic class names that would style it how you want. The Artisteer designs don't expect those regions to be there and it is very easy to break the design by adding in those extra regions because that markup is not expected or designed for. Adding those regions without breaking the design and making them blend in requires expertise of markup and CSS applied with trial and error until you are happy with the result, I know of no short cuts.