z-index & width issue with nested absolute, fixed and relative elements

Question

I am building a complex webapp using React and I'm trying to figure out the smartest way to handle a complex positioning and layering situation.

I'm wondering if I need to rethink my entire structure or just tweak some css values.

The code below explains my issues:

aside {
  position: absolute;
  top: 0;
  left: 0;
  width: 20%;
  height: 100vh;
  background: blue;
  color: white;
}
main {
  position: absolute;
  overflow: hidden;
  background-image: url('https://i.ytimg.com/vi/6sta6Gkpgcw/maxresdefault.jpg');
  background-size: cover;
  top: 0;
  left: 20%;
  width: 80%;
  height: 100vh
}
.page-wrap {
  position: relative;
  width: 100%;
  height: 100vh;
  overflow: auto;
}
.overlay {
  position: fixed;
  z-index: 1;
  padding: 40px;
  color: white;
  font-size: 24px;
  width: calc(80% - 80px);
  height: 100vh;
  background-color: rgba(0, 0, 0, .5);
}
ul {
  position: relative;
  z-index: 2;
  list-style: none;
  color: white;
  font-size: 24px;
  line-height: 2em;
  padding-top: 100vh;
}
ul li {
  display: inline-block;
  width: 200px;
  height: 200px;
  text-align: center;
  padding: 20px;
  background: #ccc;
  color: red;
  margin: 50px;
}
button {
  padding: 10px 30px;
  background: green;
  color: white;
  font-size: 24px;
}

<aside>
  SIDEBAR
</aside>
<main>
  <section class="page-wrap">
    <div class="overlay">
      <button>
        This needs to be clickable even though the list is on top
      </button>
      <div>
        <h1>My issues here are:</h1>
        <ol>
          <li>the green button is covered (disabled) by the list</li>
          <li>the overlay covers the scrollbar on its parent page-wrap section</li>
        </ol>
      </div>
    </div>
    <ul>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>6</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
      <li>vew</li>
      <li>Item</li>
    </ul>
  </section>
</main>

FIDDLE

Answer 1

My solution was to restructure the DOM so the body had the overflow. I had been trying to avoid this because it's a large webapp with a lot of components and pages, many of which suffered collateral damage, but ultimately, it solved my problem.