<div id="cone"></div>   
#cone {
  width: 300px;
  height: 200px;
background: conic-gradient(white 45deg, black 225deg, white 405deg);
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/prefixfree/1.0.7/prefixfree.min.js
  2. https://leaverou.github.io/conic-gradient/conic-gradient.js