Note: I haven't added my kit number here
I am using the Font awesome 5. I got kit script after login in the font awesome poral. My issue is, If I added below code
<!doctype html>
<html>
  <head>
    <!-- Place your kit's code here -->
    <script src="https://kit.fontawesome.com/kitnumber.js" crossorigin="anonymous"></script>
  </head>
  <body>
    <i class="fas fa-thumbs-up fa-5x"></i>
  </body>
</html>
then I am getting my icon but if I use pseudo-class then I am not getting the icon.
<!doctype html>
<html>
  <head>
    <!-- Place your kit's code here -->
    <script src="https://kit.fontawesome.com/kitnumber.js" crossorigin="anonymous"></script>
    <style type="text/css">
      .f_icon:after{
         content: "\f164";
        font-family: 'Font Awesome 5 Free';
        font-weight: 900;
        display: inline-block;
        position: absolute;
        top: 30%;
      }
    </style>
  </head>
  <body>
    <div class="f_icon"></div>
  </body>
</html>
But the above code is working if I add font awesome css without my kit.


