JSFiddle - React, Tailwind, and code Playground

HTML

<div id="pie"></div>

CSS

#pie {
    font-size: 15em;
    /* This controls the size. */
    display: inline-block;
    width: 0.5em;
    height: 0.5em;
    background:  #00cc00;
    position: relative;
    border-radius: 0.35em;
}
#pie::before {
    content:"";
    display: inline-block;
    position: absolute;
    right: 0.33em;
    bottom: 0em;
    border-width: 0;
    background: white;
    width: 0.22em;
    height: 0.12em;
    -webkit-transform: rotate(45deg);
    -moz-transform: rotate(45deg);
    -ms-transform: rotate(45deg);
    -o-transform: rotate(45deg);
}