$cssCompressor public property
CSS file compressor. If a string, it is treated as shell command template, which should contain placeholders {from} - source file name - and {to} - output file name. Otherwise, it is treated as PHP callback, which should perform the compression. Default value relies on usage of "YUI Compressor" See also https://github.com/yui/yuicompressor/.
public string|callable $cssCompressor = 'java -jar yuicompressor.jar --type css {from} -o {to}'