Several customers have had issues with the styles from our Design Upgrade Pro for H5P plugin not appearing on the frontend of their site. Things looks good in the Customizer, but the styles don’t show up on the actual website. The cause of this issue is almost always due to the server configuration.
Because of the way the H5P WordPress plugin requires us to add styles to H5P content, we have to use a .php file to load CSS code. This is a bit unconventional. Typically, you’d use a .css file to load CSS code, and a .php file to load PHP code.
I’ll explain a few things you can try to resolve this issue. It usually involves contacting your host and asking them to make a pretty simple change.