I'm having this same problem. I placed the code in my custom.css file, but the black background is still hovering over the site on my phone when I test it, and users can't access the site.
The URL for me is http://www.benefabproducts.com.
The mobile plugin does have an option to not load certain plugins, however when I deselect the pop up plugin, it's still loading it.
Would you mind checking on this for me please?