UIkit doesn’t load FA by default, the built-in icons are far nicer (IMO) but there are times when you need Font Awesome. So, I’ve found adding this to the head section in Inspector does the trick.
You need to be using https not just http.
<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.8.2/css/all.css" integrity="sha384-oS3vJWv+0UjzBfQzYUhtDYW+Pj2yciDJxpsK1OYPAYjqT085Qq/1cq5FLXAZQ7Ay" crossorigin="anonymous">
If there is a better way to do, mention it below.