JSFiddle - React, Tailwind, and code Playground

HTML

<div class="btn">Content</div>
<div class="rit"></div>

CSS

.btn {
  width: 100px;
  height: 100px;
  background: red;
  float: left;
}

.rit {
  float: left;
  width: 0;
  height: 0;
  border-top: 100px solid red;
  border-right: 100px solid transparent;
}