How to center a div (Really well) on Materialize? I've looked through over posts, but none work

I'm trying to center all the divs on my page and it's proving to be a nightmare. I managed to center the main login form with the "m3-offset" class but it's not working for the rest of the cards, any ideas? Here it is: http://eddiej.pw/ feel free to f12. Code's here: http://ift.tt/2kP33gT

Note: I spent ages searching everywhere for a answer, tried mostly all of them and the same error seemed to happen.

Thank-you!