JSFiddle - React, Tailwind, and code Playground

HTML

<div id="circle">
</div>

CSS

#circle{
    width:100px;
    height:100px;
    background:#000;
    border-radius:50%;
    margin:50px auto;
    transition:all calc(1s*2) ease;
}
#circle:hover{
    background:#555;
}