JSFiddle - React, Tailwind, and code Playground

HTML

<html>
    <head>
        <title>Mock-up page</title>
    </head>
    
    <body>
        <div id="box1">
            <div id="box2">div 2</div>
        </div>
    </body>
</html>

CSS

#box1{
    width: 300px;
    height: 300px; 
    background-color:#0000FF; 
    position: relative;
    margin-top: 30px;
}

#box2{
    margin-top: 30px;
    background-color:#008000;
    position: absolute;

}