[Theme: Motif] Reformatting Color Scheme with CSS

Hello! I just moved my website – https://www.rupertusresearch.com over to Blue Host from wordpress.com and I lost most of my formatting. I’m trying to re-do everything the way I originally had it and I’m having a lot of trouble changing some of the colors. I’m a n00b, so I tried to find a plugin that would let me do it easily, but can’t find anything that seems to work with my theme. I understand the general concept of CSS, but I can’t seem to figure out what code would help me change the entire background color of both the header and footer bar from black to navy blue. If you visit my wordpress.com site: https://www.rupertusresearch.wordpress.com, you can see the effect that I’m trying to achieve. Any help would be greatly appreciated!!