Menu Slide Content Issue

I am using a Theme call Oblique and have done quite a lot of modification to it but just want to sort one final thing out.I would like to make the menu which is already a ‘sliding’ menu to ‘push’ the pages content out of the way,rather than appearing above it.

I’ve attempted altering the z-index and positioning properties etc but am a little stuck so if anyone could point me in the right direction that would be fantastic and appreciated.

http://datset.net/home/

🙂