JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

html, body {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
}

.circle {
  border-radius: 50%;
  width: 300px;
  height: 300px;
  background-color: red;
}

.center {
  display: flex;
  justify-content: center;
  align-items: center;
  width: 100%;
  height: 100%;
}