CSS trouble

New to CSS I’ll admit, but I’m not new to code, however this has me baffled.

I have of-course Googled it but cannot find anything.

http://www.digitalpassion.co.uk/beta/

The “I am a box” divs dont stay inside the content box, but instead overlap over the bottom, suggesting an absolute position.

Is there any way around this?

thanks

StupidSaint

AKA MrChuckles