clarkwinkelmann You'd need to create an extension for that. It should be really easy.
I think of an extension, that should be easy to do as well, but with a lot more potential for developers:
Add extra classes to the body element for users logged in, for the current category, for closed and pinned discussions etc., so everyone could use these for their own CSS rules. With these classes, it would be very easy to hide the welcome message banner when logged in or to style the pages differently for each category.
Writing extensions is quite new to me and so it will take some time before I will be able to provide something in this direction. Therefore I would be pleased, if someone with better skills becomes interested.