I have been exploring the use of stacked icons with fontawesome, following a helpful blog post by Dave Gandy.
Although stacking is working well, I am facing an issue aligning a stacked icon with a non-stacked icon (which is fa-5x). It's challenging to get the size and alignment of the stacked icon to match that of the non-stacked icon. You can view the codepen here: http://codepen.io/rfiol/pen/YPQNaG
<i class="fa fa-calendar-o fa-5x"></i>
<span class="fa-stack fa-3x">
<i class="fa fa-calendar-o fa-stack-2x"></i>
<strong class="fa-stack-1x calendar-text">27</strong>
</span>