Parallax effect - make section appear behind previous section without moving content - html

Question

So what I currently have is a parallax effect that works fine, but I can't figure out how to make one section "slide up" and reveal the next section, making it look like a smooth section transition. Currently my content on the second section just keeps scrolling down until it's in its place, and I can't seem to make it appear behind the first section. I currently have this: https://jsfiddle.net/165pw4ks/3/.
index.html:
<div class="parallax-wrapper">
<div class="frame-top"></div>
<section class="parallax-section part1">
<div class="frame-bottom"></div>
<div class="part1-sticky-container">
<div class="part1-sticky">
</div>
</div>
</section>
<section class="parallax-section part2">
<div class="part2-content">
<h1 class="part2-text">
Some text here
</h1>
</div>
</section>
</div>
style.css:
body {
margin: 0;
}
.parallax-wrapper {
top: 100vh;
}
.parallax-section {
position: relative;
}
.part1 {
background: url("https://place-hold.it/1920x1080") no-repeat;
width: 100vw;
height: 100vh;
background-size: cover;
z-index: 4;
}
.frame-bottom {
position: sticky;
z-index: 100;
top: calc(100vh - 40px);
height: 40px;
width: 100%;
background-color: #111;
}
.part2 {
margin: 0;
background: url("https://place-hold.it/1920x1080") no-repeat;
background-size: 100vw;
width: 100vw;
height: 100vh;
background-attachment: fixed;
background-position: center;
background-repeat: no-repeat;
background-size: cover;
z-index: 1;
}
.part2-content {
position: sticky;
width: 30rem;
height: 5rem;
z-index: 1;
background-attachment: scroll;
background-color: transparent;
margin-left: calc(50% - 15rem);
top: calc(50% - 2.5rem);
}
.part2-text {
margin: 0;
color: white;
font-size: 32px;
text-align: center;
}
What I am attempting to make is something like on this picture:
Any help would be appreciated.