JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
    <div class="child">
        
    </div>
</div>

CSS

body {
    margin: 0;
}

.parent {
    width: 30px;
    height: 30px;
    background: red;
}

.child {
    background: green;
    width: 10vw;
    height: 15px;
}