When I scroll up from top header gets overlay

When I’m at the top of the page and I scroll up, an overlay appears on top of my header.

Where is this coming from?

Web page:

Screen recording of what happens:

If you mean the dark area above the website, this is just the standard scroll bounce effect that happens with all websites, but perhaps I am not seeing exactly what you are referring to.

ah no i mean right below it if you look at the buttons, you see them getting overlaid with the background colour and disappear a bit

but this seems to be a Safari-specific issue

I see what you are referring to - something is causing the buttons to be clipped at the top.

it is probably part of the blur that is applied to the header section