Basically the important part is that the centred div come after the left and right divs in the markup. Check out this example, it uses margin-left: auto and margin-right: auto on the centered div, which causes it to be centred.

Here: http://codepen.io/Paulie-D/pen/BuJaI

Perfect! Come to think of it, I think I had noticed that while scouring Google for a few examples, but it's importance was never pointed out so I guess I never tried it.

Thanks for the help!