JSFiddle - React, Tailwind, and code Playground

by inser

HTML

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

CSS

div {
    border: 3px solid;  
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    -ms-box-sizing: border-box;
    box-sizing: border-box;
}

.parent {
    width: 100px;
    float: left;
    height: 80px;
    border-color: black;
}

.child {
    height: 100%;
    width: 100%;
    border-color: blue;
    float: left;
}