Sidebar animation: Content area scrollbar jumps over before the animation completes #13926
Description
Describe the bug
As noted by @afercia in #13635 (comment), On systems that show scrollbars at all times, the scrollbar for the main content area does not slide over nicely when the sidebar animation occurs. Instead, it jumps over immediately, resulting in an empty white box that the sidebar animates into.
Screenshot
(The frame rate has been slowed down here to show the effect)