JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outer">
  <div class="circle">
  </div>
</div>

CSS

.outer {
  width: 300px;
  height: 150px;
  border: 1px solid black;
}

.circle {
  background-color:green;
  border-radius: 50%;
  width:50%;
  margin: auto;
}
.circle:before{
	content: "";
	display: block;
	padding-top: 100%; 	/* controls the aspect ratio */
}