margin 50px auto doesn’t work in bottom

hey guys I set margin:50px auto for body and there's only margin on top the bottom doesn't work. I can't find the problem.
http://giantgag.com/gags/so-i-heard-you-like-bad-boys-compilation?pid=2184
Also when the screen resolution is smaller the right container goes under the main content but there's still a gap on right. why it does that ?
margin 50px auto doesn't work in bottom

See original post by bondigor69