Looks like you are trying to solve the css scoping problem by inserting the application buttons directly into the shadow dom.  However, as you noticed, elements inside shadow dom are not accessible from the outside.  In order to have application elements "projected" into the shadow dom, one must use <content select="...">.  This is why I had to create a second scoped css for the buttons.  As far as I can tell, there is no way to get around that.