JSFiddle - React, Tailwind, and code Playground

HTML

<div class="test">

</div>

CSS

body{
  background:#ff0;
}
.test{
  width:300px;
  height:300px;
  border-radius:150px;
  background: radial-gradient(rgba(0, 0, 0, 0)10%, rgba(0, 0, 0, 1)80%);
}