extend bg color to the right to fill in empty space

hello,

The layout of a photoblog I’m working on has the post content on the left and a sidebar on the right. The background of the sidebar has a darker color than the body. Right now what you would see is the image on the left, darker sidebar, then lighter areas to the right of the sidebar filling in the space when the browser is opened wide.

I can’t figure out how to make it such that the darker background of the sidebar keeps extending to the right to fill in the space.

I’ve seen another website that does work like this, where using the firefox developer extension and mousing over to view the style information reveals (from left to right):
html > body > #div content
html > body > #div content > div #sidebar
html > body > #div content

Currenty my blog reveals:
html > body > #div content
html > body > #div content > #div sidebar
html > body

and the darker background stops with the sidebar.

Any thoughts on how to accomplish this? If my question isn’t clear, let me know.
thanks!