A set of dark, round buttons with a pure CSS check mark.
The check mark is created using CSS3 transforms. The button text is replaced by an empty rectangle with two borders in a
before pseudo-element. The rectangle is then rotated by 45 degrees. You can read the source here.
Also included in the snippet is a version that uses a Unicode character, which works as a fallback for browsers that don't support CSS transforms (IE 8).
Original PSD by Alex Montague.