JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outer">
    <div class="inner">Lorem ipsum dolor sit amet, consectetur adipisicing elit.<div class="fixed"></div></div>
    Lorem ipsum dolor sit amet, consectetur adipisicing elit. In illum at consectetur nam rerum asperiores nemo fuga possimus explicabo similique soluta laborum tempore illo dicta deserunt eligendi obcaecati reiciendis laudantium.
</div>

CSS

.outer {
    position: relative;
    width: 200px;
    
    background-color: #ffc;
}

.inner {
    width: 100px;

    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    
    background-color: #fcc;
}

.fixed
{
  position:fixed;
  left:0px;
  right:0px;
  top:0px;
  bottom:0px;
  background:rgba(127,127,127,0.5);
}