<div>
<span class="fa fa-html5">html5</span>
<span class="fa fa-big fa-html5">html5</span>
<span class="fa fa-big fa-red fa-html5">html5</span>
</div>
.fa { font-size: 1em;}
.fa-big { font-size: 2em;}
.fa-red { color: #f00;}