addyosmani/jquery-ui-bootstrap — comment on commit 9df8e6fa508db8e72bb8c9a40409e5277e950c7b
File: css/custom-theme/jquery-ui-1.8.16.custom.css line 675
By lightglitch:

There's still some gap the buttons in the buttonset, if you change margin-right to -4px I think looks better.