JSFiddle - React, Tailwind, and code Playground

HTML

<div id="nav"><span>icon</span></div>

CSS

#nav {
    width: 0;
    height: 0;
    border-top: 25px solid transparent;
    border-left: 50px solid #000;
    border-bottom: 25px solid transparent;
    position: fixed;
}

#nav span {
  position: absolute;
  line-height: 0;
  left: -45px;
  color: white;
}