Help adding icon to menu option

On our page, you can see that each menu button has an icon. The “Resources” tab needs to have an icon, but I can’t figure out how to add it as none of the icons are visible when I customize the menus in the theme editor. Are these something that just appear according to the name of tab? Any help is appreciated! Thanks!

• This topic was modified 3 years, 4 months ago by Jan Dembowski. Reason: Moved to Fixing WordPress, this is not an Everything else WordPress topic

The page I need help with: [log in to see the link]