If you develop your application/website using Eclipse, there is no support provided by Yahoo or the Eclipse web development platform. But, the Spket provides a good extension to fill this gap.
Their website: http://www.spket.com/ does not mention this feature, but it is smoothly integrated and very intuitive to be used.
Just right-click your css file to open the context menu and select YUI Compressor…
A Wizard is opened to browse for the target file. You can make some additional configuration and clicking OK, the minified file will be produced. Notice: You can select multiple source files and compress them into single one as well.
Please note: The Spket studio is free for non-commercial use. To support the project, the commercial use requires a usage fee of 29$ for a single user which is is a fair price.
Unfortunately, there have been no updates nor any other activity for some time. Hopefully, this will change some time again.