CSS Tweak is a web based CSS optimization tool. It will take any CSS file and optimize the syntax, grouping your style declarations into shorthand where possible. It can also remove comments, and strip whitespace for maximum compression.

The one thing that makes it different from other tools however, is you can also stop it from altering your syntactical layout at all. Instead it will go through and stick with the layout you have defined, and clean up any areas that are incorrectly formatted.

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cssTweak