Pretty ugly stuff, for combos looks like the :drop state is not on the button but on the combobox node. This totally needs to be addressed in the theme widget by widget. The inspector switch (even better an evn var) as Christoph suggest would be great indeed.

Ok, I've been able to fix something via the theme and Matthias made the behaviour saner on some widgets, the main issue here now is the textview which seems not to get the drop(active) state at all, also the textview node does basically nothing css wise, so what I can do is changing the background of the textview > text node (yeah it's gross, but at least it's something), anyway I need that state working.

the textview text node does get the :drop(active) state, and 

textview text:drop(active) { border: 1px solid red; }

works as expected