JSFiddle - React, Tailwind, and code Playground

HTML

<div id="round"></div>

CSS

#round {
    position: relative;
    width:200px;
    height:200px;
    border-radius: 200px;
    overflow: hidden;
    }
#round:before {
    position: absolute;
    content: "";
    top: -100px;
    left: -100px;
    width: 0;
    height: 0;
    border-radius: 200px;
    border: 100px solid white;
    padding: 100px;
    z-index: 2;
    }
#round:after {
    position: absolute;
    content: "";
    top: 0;
    width: 10px;
    height: 0;
    border-top: 200px solid transparent;
    border-right: 100px solid red;
    border-bottom: 200px solid transparent;
    z-index: 1;
    
}