I'm not complaining or anything, but the forum looks like this in my computer. (if you haven't noticed anything weird, just look to the right side of the image)
At the bottom of the page you will find an these icons: The one on the far left will let you toggle the width to expand to your entire screen. Edit: Just tested this myself. The background doesn't scale well to large screens. I'll see what I can do about this in the future. Edit 2: It should be fixed now!