Sticky Footer not sticky - CSS

Hi guys,

I need a sticky footer on my site - one that remains on the bottom of the browser window, but below the content (i.e. the content should push the footer down).

An example of this issue is here:
http://demo.xlearn.net.au/

I used this method for my sticky footer:
http://mystrd.at/modern-clean-css-sticky-footer/

...but for some reason it doesn't work. Could be either my HTML structure / hierarchy, or my CSS.

Any tips would be great.

Thanks!
Brett