JSFiddle - React, Tailwind, and code Playground

HTML

<div id="one">
    <div id="two"></div>
</div>

CSS

#one {
    width: 100%;
    height: auto;
    position: relative;
    float: left;
    clear: none;
    display: block;   
    background-color: blue;
}

#two {
    width: 100px;
    height: 100px;
    position: relative;
    float: left;
    clear: none;
    display: block;
    
    background-color: red;
}