JSFiddle - React, Tailwind, and code Playground

HTML

<div class="callout"></div>

CSS

.callout {
  height: 100px;
  width: 200px;
  background-color: #660077;
  border-radius: 10px;
  position: relative;
}
.callout::after {
  content: '';
  position: absolute;
  background:#660077;
  clip-path:polygon(0 0,100% 0,50% 100%);
  width:30px;
  height:30px;
  top:100%;
  right: 10px;
}