Still haven't figured it out, but found this workaround using the code block:
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
<a href="https://www.linkedin.com/company/62014" style="font-size:18px"target="_blank"aria-hidden="true" style=";color:#4a91b5"class="fa fa-linkedin"></a>
The only thing is, haven't figured out how to create hover styles since the code block seems to only allow html or CSS, not both, and the CSS injection area is being finicky in this template.