JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  <div class="z-index-9000">
    z-index 9000
  <div>
</div>

<div class="z-index-1">
  z-index 1
<div>

CSS

.z-index-1,
.z-index-9000 {
  color: white;
  position: absolute;
  top: 0;
}

.z-index-1 {
  background: orange;
  z-index: 1;
}

.z-index-9000 {
  background: steelblue;
  z-index: 9000;
}