Using and changing Menu of Platon Theme

Hi, I am trying to create a menu at your platon-theme, which I am using at a Drupal installation. I have already installed the menu_attributes modul and font awesome, but however it is not working to add icons like in Demo Version or in the Full Version of Opigno. There are only blue (or white) squares showing up with the menu title at the bottom, but no icons. If I add an icon (e.g. fa fa home) to the class field in the main menu, the little home-icon shows up next to the square and not inside of it ... How could I solve this problem? Thanks a lot. Tabea