Click expand box (animation runs over 1.8 s — plenty of time).
While the boxes are still animating, drag the scrollbar of either panel down by
~80 px.
Left panel — the red box jumps / drifts as the FLIP transform fights the scroll. Right
panel — the teal box keeps animating smoothly to its new size and stays anchored to its
place in the scrolled-content coordinate space.
