Using Font Awesome for CSS Class

Hi,
I was hoping to use font awesome to add a different icon before each menu item. So, for example the font awesome website suggests something like this for an icon <i class="fa fa-calendar" aria-hidden="true"></i>

Putting this in to the CSS Class field doesn’t work. The nearest I got it to working was adding fa fa-calendar; This resulted in the icon appearing, but unfortunately it then affected the font of the link.

Is it possible to add a font awesome icon using the CSS Class field on the Add Menu Item?

For info, I’m using “Superfish without CSS”.

Thanks.