Border around site or main content

After an hour trying variations in Additional CSS, I have to give up and ask: How does one add a border to the entire site or main content area? My header and footer have a specific color and I feel the site would look better if a few pixels of that color also bordered the space between the two (on pages, /category, /tag…everything).

A background image or background color for that area is not desired as each post/block has its own background color.

The page I need help with: [log in to see the link]