Sometime a custom element may need something like an orientation attribute to make it
vertically or horizontally (think to a slider for example), in theory it would be better
to have that as a css style instead of an attribute but currently there is no way to
observe a change in a style (being inline or in a class) so the custom element cannot
respond to it.

Is there any plan to add something like observedStyles() similar to observedAttributes()
or any other similar method to do it?

Sorry if this not the right place to ask...