Thanks
@Cableguy , after much exploring, I figured out that perhaps if...
1. I dont set the SetBackgroundImage method on the page and
2. Add
page.InjectCss($"body { background-image: url("../images/cont_bg.png") !important; background-repeat: repeat !important; }"$)
Passing the path to my image, it would work.
And it did. I guess I also need to learn some css things going forward.