JSFiddle - React, Tailwind, and code Playground

by Itay

HTML

<div class="folded">
</div>

CSS

div {
    background: #000;
    width: 200px;
    height: 50px;
    border-bottom: 3px solid red;
    position:relative;
}
div::before {
    content: "";
    position: absolute;
    height: 0;
    width: 0;
    right: 0;
    bottom: -12px;
	border-bottom: 10px solid transparent;
	border-left: 10px solid #AA0000;
}