JSFiddle - React, Tailwind, and code Playground

HTML

<div class="abc">
    <div class="bgd"></div>
  <ul class="def">
    <li>something</li>
  </ul>
</div>

CSS

.abc {
    width: 200px;
    height: 200px;
    position: relative;
}
.bgd {
    background: red;
    opacity: 0.1;
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 0;
}
.def {
    z-index: 1;
}
}