JSFiddle - React, Tailwind, and code Playground

HTML

<div id="parent">df
    <div id="child1">df</div>
</div>

CSS

html, body
    {width: 100%; height: 100%; overflow: hidden;}
    
    #parent{ 
        display: block;
        background-color: #ff0;
        border: 1px solid #f00;
        position: relative; width: 200px; 
         height:100%;
    }
    #child1{ 
        background-color: #f00; 
         display: block;
      border: 1px solid #ff0; 
        position: absolute; left: 200px;
        top: 0px; bottom: 0px;
    }