JSFiddle - React, Tailwind, and code Playground

HTML

<div class="relative-radius"></div>
<div class="fixed-radius"></div>

CSS

.relative-radius,
.fixed-radius {
  width: 200px;
  height: 100px;
  margin: 16px;
}

.relative-radius {
  border-radius: 20%;
  background-color: red;
}
.fixed-radius {
  border-radius: 10px;
  background-color: blue;
}