How to get rid of "embossed" table appearance?

I’m redesigning my homepage to include a table with links to my portfolio images (just using placeholders for now):

http://www.davesink.com/?page_id=2012

The problem is that my table has a thin line at the top, almost like an embossed look. It’s not a huge deal, but I’d like to get rid of the line if I can. I’m pretty inept when it comes to coding, but if someone could point me to the setting that might be causing this, it would be most appreciated. Would it help to provide screenshots of the stylesheet? Any changes I made to the table settings didn’t seem to make a difference. Many thanks!