JSFiddle - React, Tailwind, and code Playground

HTML

<div class="triangle">

</div>

CSS

.triangle {
  width: 0px;
  height: 0px;
  border-left: 40px solid transparent;
  border-right: 40px solid green;
  border-top: 0px solid black;
  border-bottom: 40px solid transparent;
}