Keyboard "Bracket"

[Kubbaj]

I want to add an element that mirrors what the polygon does in the wheel, but for the keyboard. I've been referring to it as a "bracket".

It should be a linear shape that sits above (or below) the keyboard, and points to each note included in the current pattern. Allowing the keys to slide left or right under it when a new tonic is chosen so that it points to the new set of notes included.

It should also itself be able to slide left or right as the wheel polygon rotates, to display alternate permutations of the pattern, similar to this:

(this will require some kind of window with overflow: invisible, and an extended bracket that can slide into view...)

[Kubbaj]

Ugh, I'm getting some weird moire or something on that gif lol