It's wins and losses plus other factors like the size of the win gap. I think you get a higher ranking boost if you win more decisively. It's also possible the game factors in player strength. So a team with weaker cards, beating a team with stronger cards *might* get a further Elo boost - because they had to overcome more for that unexpected win.

I don't know the formulas EA uses, and don't understand exactly how the ratings work, but here's a Wiki about Elo ratings that might explain  the basic concept: https://en.wikipedia.org/wiki/Elo_rating_system