JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    Container
    <div id="fixed">Child Div</div>
</div>

CSS

#container {
    width: 400px;
    background-color:red;
    position:relative;
}

#fixed {
   position:absolute;
   top:0px;
   right:0px;
   background-color:green;
}