Navbar bg to overflow to section below (updated)

This might be an unusual question. But is there any css for making the navbar background to overflow to the next section below? We want to create a seamless interaction with the graphical id of the hole site between the navbar and the rest of the website.

Url to website: https://labified.se/19-2/

This is the code we got so far. We have tried with different codes but nothing really get us on the right track.

#main-header {
Background-size: cover;
Background-repeat: no-repeate;
Background-image: url;

}

Thanks!