An excellent resource for HTML/CSS icons
Check it -> http://one-div.com
This seems to be a totally misuse of the content attribute. Cause there are better ways to display images then to tinker them out of boxes with rounded corners.
You're probably right but I feel these would be great for minimizing requests to the server increasing performance (being pure CSS), as well as being a great tool for responsive design.
There a bunch of ways to save requests like dataUri embedded images in CSS, WebFonts or embedded SVG images. All this will work far better than this hack. Also changing the font size totally break the icons after two steps.
@eskimoblood That's a very good point, thanks for the tips.