JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="subContainer">
        <div class="navParent">
            <div class="nav">hi</div>
        </div>
        <div class="changeableContent">
            <a id="contentAdd">Click me to add content</a>
        </div>
    </div>
</div>

CSS

html, body {
    height: 100%;
    margin: 0;
}
body {
    display: flex;
    flex-direction: column;
}

.container, .subContainer {
    display: flex;
    flex-direction: row;
    flex-shrink: 0;
    flex-grow: 1;
}

.navParent {
    width: 304px;
    background: black;
}
.changeableContent {
    background-color: yellow;
    flex-grow: 1;
}

JavaScript

jQuery(document).ready(function ($) {
    $('#contentAdd').on('click', function (event) {
        event.preventDefault();
        for (var i = 0; i < 100; i++)
        $('.changeableContent').append($('<p></p>').text('SOME TEXT'));
    });
});