.footer-static .footer-content .social-footer li.instagram a::before {
content: '/f16d';
}Yukarıdaki gibi kalsın, header'e şu kodları ekler misiniz?
<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.6.1/css/all.css" integrity="sha384-gfdkjb5BdAXd+lj+gudLWI+BXq4IuLW5IT+brZEZsLFm++aCMlF1V92rMkPaX4PP" crossorigin="anonymous">
ve
<script defer src="https://use.fontawesome.com/releases/v5.6.1/js/all.js" integrity="sha384-R5JkiUweZpJjELPWqttAYmYM1P3SNEJRM6ecTQF05pFFtxmCO+Y1CiUhvuDzgSVZ" crossorigin="anonymous"></script>