Thanks Rapunzl!
I already have a CSS class for a box (a div with rounded corners) it is just a question of getting it in the right place and I can't see with Firebug which the relevant file is that holds the HTML. It looks like CB generates a table into which the various core files (username etc) and plugins are inserted as rows, but I'm not sure how it does that. I'd just like to modify the appearance of that row.
It's not major but it would look better I think. I'll have another look