A method for easily stacking multiple icons. Use the fa-stack class on the parent, the fa-stack-1x for the regularly sized icon, and fa-stack-2x for the larger bottom icon. fa-inverse can be used as an alternative icon color.
fa-twitter on fa-square-o
fa-flag on fa-circle
fa-terminal on fa-square
fa-ban on fa-camera
{% highlight html %} fa-twitter on fa-square-o
fa-flag on fa-circle
fa-terminal on fa-square
fa-ban on fa-camera {% endhighlight %}