JSFiddle - React, Tailwind, and code Playground

by Douglas Santos

HTML

<div class="box"></div>

CSS

.box{
  border: 2px solid #52B3D9;
  width: 200px;
  height: 150px;
  position: relative;
  margin: 20px;
}

.box:before {
  content: "";
  position: absolute;
  top: 10px;
  left: -15px;
  border-top: 10px solid transparent;
  border-right: 15px solid #52B3D9;
  border-bottom: 10px solid transparent;
}