JSFiddle - React, Tailwind, and code Playground

HTML

<table><tr><td class="triangle">
    <div></div>
    </td></tr></table>

CSS

td.triangle {position:relative; width:100px; height:100px; background: green;}
    td.triangle div {position:absolute; right:0; top:0; width:10px; height:10px; background: red;}