That configuration property is defined in com/google/gwt/ressources/Ressources.gwt.xml that way:
<define-configuration-property name="CssResource.style" is-multi-valued="false" />
<set-configuration-property name="CssResource.style" value="obf" />
obf. I believe obfuscate or obfuscated would work too (if you find them more readable). thx i'll tryi read the mentiond doc already but the comment above the code was somehow misleading: "<!-- This can be used to make CssResource produce human-readable CSS -->"