JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
    display: inline-block;
    position: relative;
    background: #000;
    height: 200px;
    width: 400px;
    margin: 50px;
}
div:before  {
    position: absolute;
    top: 0px;
    left: 0;
    content: '';
    border-left: 0 solid rgba(0, 0, 0, 0);
    border-right: 406px solid rgba(0, 0, 0, 0);
    border-top: 106px solid #FFF;
    display: inline-block;
}
div:after {
    position: absolute;
    top: 2px;
    left: 0;
    content: '';
    border-left: 20px solid #FFF;
    border-right: 12px solid rgba(0, 0, 0, 0);
    border-bottom: 100px solid rgba(0, 0, 0, 0);
    border-top: 100px solid rgba(0, 0, 0, 0);
    display: inline-block;
}