JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

.circle {
    width: 20px;
    height: 20px;
    background: #fff;
    -moz-border-radius: 50px;
    -webkit-border-radius: 50px;
    border-radius: 50px;
    border: 2px solid #000;
    overflow: hidden;
}
.circle div{
    margin-top: 2px;
    width: 20px;
    height: 20px;
    background: #999;
    -moz-border-radius: 50px;
    -webkit-border-radius: 50px;
    border-radius: 50px;
}