Clean css - Taritsyn/BundleTransformer GitHub Wiki
BundleTransformer.CleanCss contains one minifier-adapter for minification of CSS code - CleanCssMinifier.
CleanCssMinifier is based on the Clean-css version 4.1.11.
As a JS engine is used the JavaScript Engine Switcher library. For correct working of this module, you need to install one of the following NuGet packages:
- JavaScriptEngineSwitcher.ChakraCore
 - JavaScriptEngineSwitcher.Jint
 - JavaScriptEngineSwitcher.Msie (only in the Chakra modes)
 - JavaScriptEngineSwitcher.V8
 
After package is installed and JS engine is registered, need set a name of JS engine (for example, MsieJsEngine) to the name attribute of /configuration/bundleTransformer/clean/jsEngine configuration element in the Web.config file.
To make CleanCssMinifier is the default CSS minifier, you need to make changes to the Web.config file.
In the defaultMinifier attribute of the /configuration/bundleTransformer/core/css element must be set value equal to CleanCssMinifier.