I believe this Hype demo project does what You want: test_JHSv1.hype.zip (864.7 KB)
I moved the "Ellipse" outside of the "scroll group" and had it match the movement of the "scroll group" when it first appears and slides up. The CSS is the same.
Note: Even though I left the CSS "position: sticky" in the "Head HTML" I do not think this CSS can be operational in Hype as "sticky" is a "hybrid" - "relatively" positioned until it hits a specified threshold at which point it becomes "fixed". Removing this CSS has no effect on the demo I did above as it does not rely on the CSS.