Position pop up exactly below header div (no-plugin mega-menu)

I made a mega menu with elementor pop-up. When you hover on a button in the navigation bar, a pop-up with several tabs is shown. I have good load times, am free to design the menu to my liking, but I can't get my head around one thing.

So this is the deal. I can place the pop up exactly under the navigation bar by positioning it to top and adding a margin that is exactly the height of my header.
However, my navigation bar consists of two sections and one of them is sticky.

When someone scrolls down the page and opens the mega menu, there's a space between the navigation bar and the pop-up.

Is it possible to position the pop up relative to where the navigation bar is. Without having to work with a static value for the margin. here's the link