How is style of tags at math.stackexchange done?

Question

I like the style of tags at math.stackexchange.com. In fact, I'd like to create something similar and I was wondering how are they styled.

First of all, I've launched Firebug and was trying to analyze the DOM.

Let's see i.e. [graph-theory] tag:

and in Firebug it looks like there are no brackets:

So, where's the catch?

Answer 1

You can use :before and :after classes in CSS: http://www.quirksmode.org/css/beforeafter.html.