Image Hotspots

Hi,
I want to add pop-up text to a flow diagram where I already have circles with numbers to serve as hotspots. I have tried using a transparent image in Hotspot Icon -> Uploaded Image, but the Icon displays in a white background. I am using Lumi to edit the .h5p file.

For the predefined icon, could there be a numerical option added? This way you could use icons to define numerical order, point out the order of steps, etc. 

Hello, I just noticed that H5P contents disappeared from the Admin area and navigation bar, all these contents can be shown up in the front-end, but in the admin area, they are invisible. even this page /wp-admin/admin.php?page=h5p is inaccessible to any roles who are permitted to access the admin. I have switched the theme to twenty-twenty and deactivated all plugins, H5p contents are still invisible.