JSFiddle - React, Tailwind, and code Playground

HTML

<div id="circle"></div>

CSS

#circle {
  width: 0;
  height: 0;
  border-bottom: 400px solid black;
  border-top: 400px solid black;
  border-left: 400px solid green;
  border-right: 400px solid red;
  -moz-border-radius: 400px; 
  -webkit-border-radius: 400px; 
  border-radius: 400px;
}