Hey that's strange:
- I see a sticky header on my mobile phone. Which stays on top and doesn't move (sticky) when you scroll the page.
- On Windows 10 desktop, Edge browser, I see it coming in with an animation, but disappearing as soon as you start scrolling.
- On Windows 10 desktop, Firefox, I see no header at all.
First: There is no need to do anything to 'nail' or 'stick' your header to the top. If you created a header and chosen 'top' when you created it, it will be there.
What I think: I assume you mean you don't want the header to stay on the page when scrolling? That is called a 'sticky' just like the header on this page. If I understand correct, you don't want that? Then don't set it to 'sticky'. When you edit the header in Elementor, go to the 'advanced' tab, and under 'movement effects'(might be called different, but that's what it's called in Dutch). There is the 'sticky' option. Don't set it to 'top' but to 'none'.
Furthermore, I guess it disappears because the z-index isn't set right. The z-index determines which layer is on top. The higher the number, the higher the layer. I think you must set the z-index for the header 1 or higher. Doesn't really matter, you can also set it to 9 or 99 or so, as long as it is higher than the other elements. This setting is found under advanced tab> advanced.
Hope this helps. Nice site, by the way.