JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
    height: 300px;
    background: url('http://images2.layoutsparks.com/1/190037/serene-nature-scenery-blue.jpg');
    position: relative;
}

div:before {
    content: '';
    position: absolute;
    top: 0; right: 0;
    border-top: 80px solid white;
    border-left: 80px solid rgba(0,0,0,0);
    width: 0;
}