Sidebar background color & padding/margin problems

I am very new to wordpress and I am going out of my mind with this problem.

My website:

In the left sidebar (apparently it’s called primary sidebar) I have placed a Facebook widget. No matter what I do, I can’t seem to change the background color to white.

I tried to change padding and margin settings in style.css and I use a child theme. I use twenty fourteen and thus copy/paste from that stylesheet, and only make changes in the child theme, so that nothing is changed in the root.

Please, can anyone tell me, what to do?