Sticky item needs sibling factor, is a hoax.

https://gyazo.com/2dafa7207edd4878b119547db6274acc

The statement "sticky item needs sibling element" is NOT TRUE. It works without sibling elements, as shown on the right above.

A sticky container may fit into a sticky item when there is no sibling element. In that case, it does not move because there is no space to move.

So "sticky containers need to be spread out over the area where you want the sticky item to move" is correct.

In the above example, the flexbox effect is spreading without doing anything in particular, and for demonstration purposes, only the left side has been shrunk with height: fit-content.

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