How do I use an image instead of the line for a border on the top and bottom of my site? I want it to have the curved corners but I cannot figure out how to implement it anywhere, what I am saying is that I have a 4px border on both left and right but I want an image for top and bottom like this site http://jenniejdesigns.com/testjj2.html I can do it in html but how do you do it with css? what file do I need to edit then?

thanks
Avie