Integration of Xtypo css in Tinymce Editor

I have insyalled the Xtypo Buttons plugin on a new Joomla 3.9 site and everything works except that the styling applied does not show in the Tinymce editor.

I have installed the required css in my template css file, and also tried it in the template custom.css file. Neither made any difference in the Tinymce editor. I have also added the span[class] statement to the editor's extended elements.

Comments appreciated.

OK, that's fine, we all do these things when busy!

No, I cannot resolve this problem and would appreciate your help. I have spelled out the details in my other recent post.