Stacked icons:
fa-twitter on fa-circle-thin
fa-twitter (inverse) on fa-circle
fa-ban on fa-camera
Use of large icon class on parent element (fa-lg):
fa-twitter on fa-circle-thin
fa-twitter (inverse) on fa-circle
fa-ban on fa-camera
Use of larger icon class on parent element (fa-3x):
fa-twitter on fa-circle-thin
fa-twitter (inverse) on fa-circle
fa-ban on fa-camera