Followings are the list of popular Pure CSS icons libraries.
Every icon has its own class.So,you have to place the icon class to the <i>
element base class.
Font Awesome :
<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.6.3/css/all.css">
Bootstrap :
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
Google Material :
<link rel="stylesheet" href="https://fonts.googleapis.com/icon?family=Material+Icons">
General Syntax
<i class="custom-alignment--concept"></i>
<i class="material-icons xsmall">cloud</i>
<i class="glyphicon glyphicon-cloud small"></i>
Source Code
<i class="custom-alignment--concept"></i>
<i class="fa fa-handshake-o" aria-hidden="true"></i>
<h3>Google Material Design Icons</h3>
<i class="material-icons xsmall">cloud</i>
<i class="material-icons small">cloud</i>
<h3>Bootstrap Icons</h3>
<i class="glyphicon glyphicon-cloud xsmall"></i>
<i class="glyphicon glyphicon-cloud small"></i>
Source Code : Output