I initially posted how to do this through cpanel, but found that the problem was a couple of elements that covered the page was hiding my background image. I have another post below that tells everything I did in the custom css in the admin panel. The image in that css file is an image from a web address that I was just using to test, so it will show on you site just by copying and pasting the entire code in your custom css. You can play around with the colors. The rgba colors I used use regular rgb colors with an alpha channel at the end to add the opacity. The alpha channels are 0.1 - 1. You will see that at the end of the color.