Leviathan Theme and Overflow

I’m trying to get this website’s (http://www.atroxen.com/jzschau) horizontal overflow to work correctly. When I reduce the size of the browser window, no horizontal scroll bar appears. This makes it very difficult to read the page when the window size is reduced or on a computer that’s very low resolution.

I’m using the Hybrid-Leviathan theme. It appears as if the theme itself does not function correctly either. Any ideas? I can force the bar to appear by changing the .css overflow to visible, but auto does nothing.

The theme demo can be found at: http://themehybrid.com/demo/leviathan/

As you can see, the same problem exists there too.

Any ideas? Below is the code that I think needs changing (i.e. changing the overflow to visible makes the scroll bar appear, but I don’t want it there all the time (only when needed).

Thanks!

#body-container {
overflow: hidden;
width: 100%;
background: transparent url(images/bg.jpg) repeat-x 0 0;
}