Q:

No Font-Awesome icons of theme

Can anybody tell me how to set up Font Awesome to work with a theme? 
I have put this in my template file: 
    <div id="social-media-bar" class="container">
    <div class="row">
        <div class="col-md-2 col-md-offset-2">
            <i class="fa fa-linkedin-square fa-3" aria-hidden="true"></i>
        </div>
        <div class="col-md-2">
            <i class="fa fa-facebook-square fa-3" aria-hidden="true"></i>
        </div>
        <div class="col-md-2">
            <i class="fa fa-xing-square fa-3" aria-hidden="true"></i>
        </div>
        <div class="col-md-2">
            <i class="fa fa-twitter-square fa-3" aria-hidden="true"></i>
        </div>
    </div>
</div>

But there are no icons loaded. They aren't loaded in admin mode either but the IP menus have their FA icons as they should. 
What am I doing wrong? Are some LESS entries necessary in my theme?

A:

I have used Bootstraps CDN in the head now: 
<link href="https://maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css" rel="stylesheet" integrity="sha384-wvfXpqpZZVQGK6TAh5PVlGOfQNHSoD2xbE+QkPxCAFlNEevoEH3Sl0sibVcOQVnN" crossorigin="anonymous">

