CSSTidy is an open source Cascading Style Sheets parser and optimiser written by Florian Schmitz. There are C++ and PHP versions available for download if you really want to go that route.
CSSTidyOnline.com is an online version of CSSTidy. Well, one of the many. There are several for you to choose from if you don't like this site.
For more information on the CSSTidy Project, please visit the project page.