Designer does not accept style sheet from the resource file, I will always get "invalid style sheet" error.
If I copy the QSS file content directly to "Edit Style Sheet" dialog it's valid and works fine, also style changes are seen immediately in the designer.

Resource file should be ok, since I can use it from the code and style changes are reflected to widget.

Am I missing some steps or is this bug in the Designer?

Added a small example which demonstrates the problem.