How do I change Body color?

Hey there! I want to use a background image with the dark theme. However, when I do that the dark theme adds a block that covers the background theme, so I figured I could just use the Light theme and change the color of the header, body and footer. I got the header and footer to change the color but I can't seem to find how to change just the body color. Is there a Custom CSS code for it or do I have to dig in the stylesheet?