JSFiddle - React, Tailwind, and code Playground

HTML

<div id="triangle" />

CSS

#triangle {
    position:fixed;
    background: purple;
    width :0px;
    height:0px;
    border-left: 50px solid transparent;
    border-right: 50px solid transparent;
    border-bottom: 50px solid red;
    border-top: 50px solid transparent;
}