Can't hide fixed navbar with z-index - html

Question

I'm currently trying to create an effect - imagine a fullscreen image which is fixed and will be hidden below the content div on scroll (parallax). Additionally I want the navbar to not move on scroll, hence it's fixed. But I want the navbar to also be hidden below the content div as soon as it's being reached on scroll.
Therefore I've tried to use z-index, but without success. Somehow I'm not able to hide the fixed navbar below the content div.
Header:
<div class="container-fluid position-fixed">
<div class="row m-0 w-100">
<div class="col-2 justify-content-center d-flex offset-5">
<a class="align-self-center" routerLink="">
<h1>NØREBRO STUDIOS</h1>
</a>
</div>
<div class="col-5 pl-5">
<ul class="nav justify-content-start">
<li class="nav-item mr-5">
<a class="nav-link" routerLink="cases">Work</a>
</li>
<li class="nav-item mr-5">
<a class="nav-link" href="#">About</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Contact</a>
</li>
</ul>
</div>
</div>
</div>
CSS:
.container-fluid {
z-index: 1;
background-color: transparent;
padding: 3em 0em;
}
Content (upper-container is supposed to hide the header on scroll):
<div class="container-fluid px-0">
<app-transparent-header></app-transparent-header>
</div>
<div class="front-image min-vh-100 min-vw-100">
</div>
<div class="container-fluid upper-container">
...
CSS:
.front-image {
background-image: url("/assets/images/savum/savum-front.png");
background-position: center;
background-repeat: no-repeat;
background-size: cover;
background-attachment: fixed;
}
.upper-container {
padding: 15em 15em 0em 15em;
background-color: blue;
}
.container-fluid {
z-index: 9999;
}

Answer 1

If I understand correctly, you want the header to be hidden but you want the navigation bar to be fixed the top of the screen when you scroll:
.nav-parent {
position: sticky;
position: -webkit-sticky;
top: 0;
z-index: 999;
}
Set a parent class over the navigation bar, and assign it those values