Non Composited Scroller In Sticky

This turquoise box is a position: sticky box. The black-and-white scroller beelow has a clip region so should be non-composited. The document has scrolling of its own.

Scroll the document down so the turquoise box is not quite aligned with the viewport top but enough that the scroller below no longer overlaps its original position. Now attempt to scroll over the black-and-white scroller with wheel or touch. If box must scroll; the document must not scroll.

Continue to scroll the document down so the turquoise box becomes fixed to the viewport top. Now attempt to scroll over the black-and-white scroller with wheel or touch. It should scroll as before, the document must not scroll.