Is it possible to format the font used for custom navigation links?

I put only the fontawesome icon here

a[href="/category/assistenza"]:before {
  display: inline-block;
  font-family: FontAwesome;
  font-style: normal;
  font-weight: normal;
  line-height: 1;
  content: "\f0fa";
  margin-right: 3px;
}

and only for the Assistance button. I add the Chat icon right now.
BTW I can see them without adding anything on mobile CSS.
(I delete all the mobile CSS in that stylesheet and I can still see the links on mobile and they are ok.)

They works on mobile only with the script that I add in body (in which tab you add the script @ron_jeremy?)