JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

html, body {
    height: 100%;
    margin: 0px;
}

body {
    display: flex;
    flex-flow: row wrap;
    align-items: stretch;
}

#first {
    flex: 1 0 200px;
    background-color: red;
}

#second {
    flex: 1000 0 200px;
    background-color: blue;
    min-height: 200px;
}

JavaScript

var second = document.getElementById("second");

document.onclick = function () {
    var p = document.createElement("p");
    p.textContent = "Content";
    second.appendChild(p);
};