JSFiddle - React, Tailwind, and code Playground

HTML

<div class="bordered">1</div>
<div class="square">2</div>

CSS

div {
    margin:10px;
}
div.bordered {
    border: 4px solid #f66;
}
div.square {
    width:100px;
    height:100px;
}

div:hover {
    box-shadow:0 0 4px #0f0;
}