JSFiddle - React, Tailwind, and code Playground

HTML

<div id="box">
  <div id="icon">
    |&gt;
  </div>
  Contents of the box
</div>

CSS

#box {
  position: relative;
  width: 200px;
  height: 200px;
  padding: 10px;
  margin: 100px;
  background-color: white;
}

#icon {
  background-color: green;
  color: white;
  padding: 10px;
  width: 20px;
  height: 20px;
  position: absolute;
  right: -20px;
  top: -20px;
}