CSS editor for site users?

I really have no idea how to ask this question (so if you have any suggestions for a better thread title, please post them), but here is the deal…

I am creating a “banner system” where ‘advertisers’ are allowed to set the text for the banners that changes every day (it’s for a lunch menu). I’m having trouble with allowing them to change the text format in the banner.

I wish it was as simple as giving them a textbox and allowing them to put in the CSS as they want it (for example)
[FONT=Verdana][SIZE=2][FONT=Verdana] color:#FFFFFF; text-align:left; font-family:serif; font-style:italic;[/FONT][/SIZE][/FONT]
But of the restaurant owners using the site are NOT experienced with CSS, so this might be a bit tough for them.

I am not sure what to do at all. Any ideas?