Mostly just an experiment to stare at.
This patch changes panel sections so that the titles are shown as contained inside their sections when opened. With the current behavior it can sometimes not be obvious which section belongs to each title or subtitle.
A capture explains this better. The left shows how it looks now, the right how it looks after this patch is applied:
By changing the background color of the open section title, it better becomes a title for that section. The separation is clearer, the title serves its purpose a bit better. It seems to work even better as complexity is added. It is much clearer what "Bounds" is in the right capture.
Note that I also remove the right-side "drag" handle for open sections. So you can't drag an area while open. That may or not be a big deal, but I just thought it looked nicer like that.