bootstrap glyph icon mail code example
Example 1: bootstrap glyphicons
<link rel="stylesheet" href="//netdna.bootstrapcdn.com/bootstrap/3.0.0/css/bootstrap-glyphicons.css">
Example 2: glyphicons in bootstrap 4
<div class="panel panel-primary">...</div>
<div class="panel panel-success">...</div>
<div class="panel panel-info">...</div>
<div class="panel panel-warning">...</div>
<div class="panel panel-danger">...</div>