Pure CSS Parallax + Navigation Reveal on Scroll

So I've run into a problem involving pure CSS parallax in combination with a fixed navbar that changes size when the page begins to scroll or returns to the top. Each of the two parts work independently but when I combine them the parallax effect still works while the navbar does not change from it's initial state.

Here is the code for the parallax:

main {
  perspective: 1px;
  transform-style: preserve-3d;
  height: 100vh;
  overflow-x: hidden;
  overflow-y: scroll;
}

header {
  display: flex;
  flex: 1 0 auto;
  position: relative;
  z-index: -1;
  height: 100vh;
  justify-content: center;
  align-items: center;
  transform: translateZ(-1px) scale(2.25);
  background: url('https://faith.prismapixel.studio/assets/img/hero-desktop.jpg') top center / cover;
}

section {
  position: relative;
  display: block;
  background: #FFFFFF;
  z-index: 1;
}

section article {
  max-width: 75rem;
  margin: 0 auto;
  padding: 7.5rem 0;
}

p {
  margin: 7.5rem 0;
}

<main>
  <header class="section parallax">
    <h1>HEADLINE HERE</h1>
  </header>
  <section class="section static">
    <article>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
    </article>
  </section>
</main>

And here is the code for the navbar:

window.onscroll = function() {
  yScroll()
};

function yScroll() {
  if (document.body.scrollTop > 10 || document.documentElement.scrollTop > 10) {
    document.getElementsByTagName('nav')[0].className = "mini";
  } else {
    document.getElementsByTagName('nav')[0].className = "";
  }
}
window.addEventListener("scroll", yScroll);

nav {
  position: fixed;
  z-index: 9;
  top: 0;
  left: 0;
  width: 100%;
  height: 0rem;
  background: #FFFFFF;
  opacity: 0;
  color: #FFF;
  font-size: 23px;
  transition: height 0.3s ease 0s, opacity 0.3s ease 0s;
  overflow: hidden;
}

nav.mini {
  opacity: 1;
  height: 3rem;
}

header {
  display: flex;
  flex: 1 0 auto;
  position: relative;
  z-index: -1;
  height: 100vh;
  justify-content: center;
  align-items: center;
  transform: translateZ(-1px) scale(2.25);
  background: url('https://faith.prismapixel.studio/assets/img/hero-desktop.jpg') top center / cover;
}

section {
  position: relative;
  display: block;
  background: #FFFFFF;
  z-index: 1;
}

section article {
  max-width: 75rem;
  margin: 0 auto;
  padding: 7.5rem 0;
}

p {
  margin: 7.5rem 0;
}

<nav class="">

</nav>
<main>
  <header class="section parallax">
    <h1>HEADLINE HERE</h1>
  </header>
  <section class="section static">
    <article>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
    </article>
  </section>
</main>

As you can see they both work fine on their own. If I remove the styling for the <main> tag, then the navbar will work but the parallax effect won't.

What am I doing wrong?

After a bit of scouring the web and teaching myself more about javascript I have solved my dilemma.

function yScroll() {
  var el = document.getElementById("main");
  var nav = document.getElementById("navBar");
  var y = el.scrollTop;
  if (y >= 50) {
    nav.className = "mini";
  } else {
    nav.className = "";
  }
}

html {
  font-size: 10px;
  scroll-behavior: smooth;
  color: #212121;
  box-sizing: border-box;
  line-height: 1.4;
  margin: 0;
  padding: 0;
  min-width: 32rem;
}

body {
  font: normal 400 1.5rem 'Montserrat Alternates';
  background: #ffffff;
  margin: 0;
  padding: 0;
  height: 100%;
  width: 100%;
  position: absolute;
  top: 0;
  left: 0;
  overscroll-behavior-y: none;
}

nav {
  width: calc(100% - 1rem);
  height: 0rem;
  position: fixed;
  top: 0;
  left: 0;
  z-index: 9000;
  text-transform: uppercase;
  transition: all 150ms ease 0s;
}

nav.mini {
  background: #FFFFFF;
  height: 5rem;
  box-shadow: 0 0 .5rem 0 rgba(0, 0, 0, .15);
}

#main {
  perspective: 1px;
  transform-style: preserve-3d;
  height: 100vh;
  overflow-x: hidden;
  overflow-y: scroll;
}

#main::-webkit-scrollbar {
  width: 1rem;
}

#main::-webkit-scrollbar-track {
  -webkit-box-shadow: inset 0 0 .5rem rgba(#212121, .5);
}

#main::-webkit-scrollbar-thumb {
  background-color: darkgrey;
  outline: 1px solid slategrey;
}

header {
  background: url('https://faith.prismapixel.studio/assets/img/hero-desktop.jpg') top center / cover;
  display: flex;
  flex: 1 0 auto;
  position: relative;
  z-index: -1;
  height: 100vh;
  justify-content: center;
  align-items: center;
  transform: translateZ(-1px) scale(2.25);
}

section {
  position: relative;
  display: block;
  background: #FFFFFF;
  z-index: 1;
}

section article {
  max-width: 75rem;
  margin: 0 auto;
  padding: 7.5rem 0;
}

p {
  margin: 7.5rem 0;
}

</style>

<nav id="navBar" class="">
</nav>
<main id="main" onscroll="yScroll()">
  <header>
    <h1 id="print">Headline Here</h1>
  </header>
  <section>
    <article>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
      <p>ʻO Lorem Ipsum kahi haʻahaʻa wale nō o ka paʻi a me keʻano o nāʻoihana. ʻO Lorem Ipsum ka 'ōlelo papahana maʻamau o kaʻoihana o ka makahiki 1500, i ka wā i lawe ai kekahi mea paʻi kiʻiʻole i keʻano o ka type a scrambled iā ia e hana i kahi puke
        kiko'ī. ʻAʻole i ola wale i kaʻelima mau kenekulia, akā,ʻo ka leleʻana hoʻi i nāʻano o ka lolouila, e hoʻololiʻoleʻia ana. Ua hoʻolahaʻia i nā makahiki 1960 me ka hoʻokuʻuʻana i nā pepa Letraset i loko o nā moʻolelo Lorem Ipsum, a me nā mea hou
        aku me ka polokalamu hoʻopuka pākī e like me Aldus PageMaker me nā papa o Lorem Ipsum.
      </p>
    </article>
  </section>
</main>

I had to modify the width of the navbar after solving my dilemma to accommodate the width of the scrollbar due to the scrollbar actually being on the <main> element and not the <body>. But that was easy to do.

I hope this helps anyone else trying to add a fixed reveal on scroll navbar to a pure CSS website.