[totaltec]

Martin,
I think the best way would be to change the way the tabs are called, adding a class to that particular tab. I don't have the custom tabs module to check, but I expect there is a php file that defines the tab and passes it to the template. I also imagine that you have an admin interface to assign new tabs. To do this properly I think you would need to add to the admin interface a place for class, create a field in the database to hold the class name, reference that field in the php file that builds the tab, and finally assign the class in the template.

Not an easy task.