Hey guys!

If you go to Twich.tv and in the middle you will see this image navigation bar. Is it HTML or CSS and how could I make something like it? I made the image nice and big so here is the URL: http://i49.tinypic.com/2z9l2ww.png

How would I make something like that where you put your mouse over it and it darkens.

Thank you guys so much for your time!