thank you, good work!
before we merge this, something to discuss:
personally, I would prefer the attribute to be a Boolean attribute, which disables the indicator when it is present.
maybe something like noindicator or plain.
@sole what do you think?

Oh, that'd be really good, actually :)
Is there a good example of being able to modify the DOM via inspector or interact with a brick widget via JS from outside? I'd like it to be a property you could toggle display:hidden vs just not animating it

noindicator is the form I prefer more

I think I've got a better grasp on this now, revised to use noindicator to change the display property, left it still animating s.t. it'd be in the right place if noindicator attr is removed

we might be able to simplify the code by just adding:

brick-tabbar[noindicator] .selected-indicator {
  display: none;
}

to the default theme css file.
and just always have and animate the indicator. The themes can then make use of the noindicator attribute to either display it or not.
what do you think about that?

haha, yeah, that makes a lot more sense 👍