Footer widgets, how to make them stack responsively rather than side by side?

Hello!
The theme is working really well on this new site I created, we just have one pending issue with the footer.

I’m using the three footer widgets and when I view the site in a smaller device the footer elements stay side-by-side rather than stacking, which makes the body background wider (to the right) than the body content… See here.

Any advice for what I need to change in order to have them stack or respond better to small devices would be GREAT!!

Thanks in advance!
-Ana