JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
    background: green; /* W3C */
    position: relative;
    z-index: 10;
    width: 30%;
    height: 200px;
    float: left;
    margin-right: 3%}

div:before {
    content: "";
    height: 0;
    width: 0;
    border-top: 200px solid red;
    border-right: 200px solid transparent;
    position: absolute;
    top: -20px;
    left: -10px;
    z-index: 20;
}

div:after {
    content: "";
    height: 200px;
    width: 200px;
    background: blue;
    position: absolute;
    top: -20px;
    left: -10px;
    z-index: -1;
}