Not Showing Up

I’ve tried this plugin in various environments (3 different servers/Wordpress installs, older version of WP and latest version, various child themes, various devices and browsers) and haven’t been able to get it to work once.

The icons don’t show up on the front end of the website, and they also don’t show up on the back end (for example, on the settings page, they don’t show up in the Live Preview area).

Am I missing something?