<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<h4>.btn-circle .btn-sm</h4>
<button type="button" class="btn btn-facebook btn-circle btn-sm"><i class="fa fa-facebook"></i></button>
<button type="button" class="btn btn-twitter btn-circle btn-sm"><i class="fa fa-twitter"></i></button>
<button type="button" class="btn btn-dropbox btn-circle btn-sm"><i class="fa fa-dropbox"></i></button>
<button type="button" class="btn btn-github btn-circle btn-sm"><i class="fa fa-github"></i></button>
<button type="button" class="btn btn-google btn-circle btn-sm"><i class="fa fa-google"></i></button>
<button type="button" class="btn btn-vk btn-circle btn-sm"><i class="fa fa-vk"></i></button>
<h3>.btn-circle</h3>
<button type="button" class="btn btn-default btn-circle"></button>
<button type="button" class="btn btn-primary btn-circle"></button>
<button type="button" class="btn btn-success btn-circle"></button>
<button type="button" class="btn btn-info btn-circle"></button>
<button type="button" class="btn btn-warning btn-circle"></button>
<button type="button" class="btn btn-danger btn-circle"></button>
<h2>.btn-circle .btn-lg</h2>
<button type="button" class="btn btn-default btn-circle btn-lg"></button>
<button type="button" class="btn btn-primary btn-circle btn-lg"></button>
<button type="button" class="btn btn-success btn-circle btn-lg"></button>
<button type="button" class="btn btn-info btn-circle btn-lg"></button>
<button type="button" class="btn btn-warning btn-circle btn-lg"></button>
<button type="button" class="btn btn-danger btn-circle btn-lg"></button>
