Site: http://www.toolsforchrist.com/shop

I am trying to make the top menu bar always highlight the "Shop" link when in the shopping section of the website, by having a white background. I could not get this to work in the CSS so I just created an image. But now the it makes the text messed up. I probably went about this the wrong way, with my limited programming language. Does anyone know the best way to accomplish this?

Thanks for the help
Corey