User 1 CSS is causing horizontal scrolling

Thanks for this great theme. I modified it with a wrapper around the sidebar and main content of the body (so the wrapper encapsulates these 2 divs), to add a faux column. When I'm logged in as user 1, the whole wrapper has horizontal & vertical scrollbars, whether they need them or not. I can't see a tag in the user1 css that impacts height, width, or would add margins that cause the area to fall outside of my fixed-width faux wrapper, but obviously I've missed something. If you have any suggestions, they're much appreciated - thanks.