Make break periods in bottom timeline transparent

[OliBomby]

closes #29339

Break periods in the bottom timeline are also transparent in stable. I chose the color and alpha on what looked right to me.

[bdach]

Not sure. I'd probably also accept kiai markers showing on top of break markers?

Seems probably fine to me, but I'm not merging without @peppy crosscheck since he has his opinions on how the bottom timeline should look that I'm not confident of being able to match.

[peppy]

I'd probably also accept kiai markers showing on top of break markers?

I'd prefer this. I'll have a play with it.

[OliBomby]

I'd probably also accept kiai markers showing on top of break markers

We have to be careful to not create the inverse problem of breaks being hidden by kiai times on the bottom timeline.

[peppy]

I've updated the visuals of this a bit:

@bdach sanity sign-of please.