CSS Compressor and Minifier is the best tool for compressing or minifying your CSS files online. It gives you the maximum number of configuration options for compressing your CSS files. The detailed description about configuration options is written under "doc". This online tool can also be used to properly indent or align or format your styling rules inside your CSS. Moreover, it has been designed considering all browsers till date(including IE5 and below) as well as all upcoming browsers in future. It also takes care of the 'Box Model Hack', thanks to YUI Compressor.