JSFiddle - React, Tailwind, and code Playground

HTML

<div class="content">
    <div class="corner"></div>
</div>

CSS

.content {
    position: relative;
    width: 300px;
    height: 300px;
    background: #ccc;
}
.content.big {
    width: 500px;
}

.corner {
    position: absolute;
    top: 0; right: -10px;
    bottom: 0;
    width: 10px;
    background: #000;
    cursor: pointer;
}

JavaScript

var $content = $(".content");
var $corner_button = $(".corner");
var MOD = "big";

$corner_button.on("click", function () {
	toggleBig();
});

function toggleBig () {
	$content.toggleClass(MOD);
}