JSFiddle - React, Tailwind, and code Playground

HTML

<button id="add">Add Content</button>
<div class="content">
    <p>Main content goes here.</p>
</div>
<footer class="smallFooter">
    <p>Footer content goes here</p>
</footer>

CSS

html, body {
    height: 100%;
}
body {
    display: table;
    width: 100%;
}
.content {
    display: table-row;
    height: 100%;
}
.smallFooter {
    display: table-row;
    height: 1px;
}

JavaScript

$("#add").on("click", function() {
  $("<p>Main content goes here.</p>").appendTo(".content");
});