Replace :before with :after

The sort arrow being right, it makes more sense to use the pseudo-element after.

And if first:letter is used, the pseudo-element before is a problem.
When the :first-letter is apply to an element having content generated using :before, it apply to the first letter of the element including the generated content. 

http://www.w3.org/TR/CSS21/selector.html#before-and-after