I too, would also like to have a look at Tom’s (secret) CSS for BBpress.
There are a couple of plugins in the WordPress repository that will get you started:
BBP style pack
The other thing you can do is use firebug. Just view you site in firefox then press F12. Then click on the small window icon left bottom so that it is blue. Then right click on what ever element you want to modify. To the right you will see its unique css element identified. You can use that in your custom css and style it how you desire.