Hi,
I did a quick demo to show the issue.
Scrollsmoother works great, as it promise.
On a production site of a customer I hade to add a second wrapper, being that only after a deep read I found that it adds a position fixed to the original wrapper. (works a bit like LocomotiveJs with matrix transform while scrolling).
I found a problem which I cant solve: fixed elements dont stay fixed at all.
Example: nav menu should stay there, and also the scrolltop on the demo, should stay at bo