JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
  width: 150px;
  height: 50px;
  background-color: #999;
  margin-left: 40px;
  border-radius: 4px;
  position: relative;
}

div:before {
  content: '';
  position: absolute;
  left: -25px;
  top: 6px;
  border: 13px solid;
  border-color: transparent #999 transparent transparent
}