JSFiddle - React, Tailwind, and code Playground

HTML

<div id="demo"><div id="zemo"><div id="remo"></div></div></div>

CSS

div {
    display: flex;
    width: calc(100% - 4em); 
    height:calc(100% - 4em);
    border: 1em solid blue; 
    border-radius:50%;
    margin: auto;
}
div#demo { width:12em; height:12em; }
div#zemo { width:9em; height:9em; }
div#remo { width:5em; height:5em; }