JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="first"></div>
    <div id="second"></div>
</div>

CSS

#container {
        width: 50px;
        height: 100px;
        border: 1px solid red;
        position: relative;
    }
    #first {
        position: absolute;
        width: 100%;
        height: 20px;
        border: 1px solid blue;
    }
    #second {
        width: 100%;
        position: absolute;
        top: 20px;
        bottom: 0;
        border: 1px solid green;
    }