Font Awesome Circle Background

HTML

<link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/font-awesome/4.2.0/css/font-awesome.min.css">
<span class="fa-stack fa-5x">
  <i class="fa fa-circle fa-stack-2x icon-background4"></i>
   <i class="fa fa-circle-thin fa-stack-2x icon-background6"></i>

  <i class="fa fa-lock fa-stack-1x"></i>
</span>

<a href="#">
  <span class="fa-stack fa-lg">
  <i class="fa fa-circle fa-stack-2x icon-background5"></i>
  <i class="fa fa-facebook fa-stack-1x"></i>
</span>
</a>

CSS

.icon-background4 {
    color: #c0ffc0;
}

.icon-background6 {
    color: #40c040;
}

.icon-background5 {
    color: #c0c0ff;
}