Solid rounded corner background for post column only

Hi there,

I’m wondering if someone can help me with adding code to put a white background behind the post column in the theme I’m testing here: http://www.auntiepea.com/testing/

Ideally I’d like the top of the posting column to have rounded corners. I can create a rounded corner image to start with but seem to be baffled at how to add it followed by a background of all white behind the posts themselves.

Any help would be MUCH appreciated.

Thanks in advance!