I kept trying to change the background-color in customizer, but no matter what I set it to it wouldn’t change. Taking a screenshot, the color was almost white (#FDFDFD). I finally looked in customizecss.php and realized the line below (line #241) was incorrect.
The actual class for the page source is .fr-contents. Below is the corrected code. Tested this and I can now change the background-color. Please include in your next update.