Changing Footer background color using CSS

Howdy:
In twentythirteen, I want to change the background color of both the footer and the navbar. I have used Chrome Web Developer to inspect both these elements and find out what class and ID they are determined by. I am able to get them to change using Web Developer. I have entered new values for these same elements in my child theme’s CSS. It doesn’t work. I can only get the background colors to change if I go into the main theme’s parent CSS file and change it in there. Obviously this isn’t ideal, but also I simply don’t understand why my child theme CSS changes aren’t working. I am successfully using the child CSS page to style other elements on this site.