Body background image on tablet and mobile not displaying?

I have a background image set on my body. I made a small section that is transparent so that as you scroll past it reveals the image. It works fine on desktop but does not display on tablet or mobile versions. It looks fine in the webflow designer though? Is this the right technique to use for this kind of effect? Or am I missing something?
here is the link: davidrobertswebdesign.webflow.io


Here is my site Read-Only: [LINK][1]
([how to share your site Read-Only link][2])


[1]: http://
[2]: https://university.webflow.com/article/sharing-your-sites-read-only-link