JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

#main {
    height: 600px;
}

#one {
    display: flex;
    height: 100%;
    flex-direction:column;
}

#two { 
    flex: 1;
    background-color: dodgerblue;
}