If you want to find out what the exact class is that you want to edit, you could use Firebug and then select the field you want to edit.
When an item is selected in the templategrid, the class of the item will change (note the different colour for instance).
These classes can all be edited by changing your layout.css file. If you can't find the classes there, you must add them yourself.
It is important, though, that you do this properly. If you want to add a class in 2.5.x, you have to use .tundra .myCustomClass { define here }, but if you use 3.0 you have to use .default .myCustomClass { define here }.
I hope this helps :)