Any way to change header icon in CSS?

I liked the basic version of the Arcade theme, so I purchased the full version. In trying to set up the full version, though, I’m finding that not all the header icons that were available in basic are showing up in the full version 🙁 I really want to use battery-quarter. Does anyone know a way to edit the CSS to change this? I’m new to WP so am still a bit confused by everything.

I did put in a support request to the people who sell the theme, but I have to wait for a response, and I’d like to solve this sooner rather than later.

Thanks 🙂