On my chemistry site www.mychemistrytutor.com there is an overlap in the middle of the page. I can not figure out how to get it to go away.
Don't force heights, especially when the contents at default font size will overflow. Taking out "height: 200px" from the layers "box2" and "box3" will solve the problem. Also, if you are using Firefox, Firebug is a great extension when it comes to debugging cases like these.