JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="fixed">
    <div class="absolute">
    
    </div>
  </div>
</div>

CSS

.container{
  width:100%;
  height:500px;
  background-color:#ddd;
}
.fixed{
  position:fixed; 
  width:100%;
  height:50px;
  background-color:red;
  top:8px;
  left:8px;
  right:15px;
}
.absolute{
  position:absolute;
  height:100%;
  width:100%;
  background-color:green;
  top:51px;
  left:0px;
}