Release Notes:
* Fixed the behavior of panel buttons when their panel is open. Show the
key binding for closing the containing dock (preview only).
* Improved the styling of zoomed panels and panes, giving them a
stronger border, and color the zoom button with an "active" style
(preview only).
* Improved the stability of panels' zoom state. Close their dock instead
of resetting their zoom state when dismissing panels to reveal other
items (preview only).
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