JSFiddle - React, Tailwind, and code Playground

HTML

<div class='red border'></div>
<div class='green border'></div>
<div class='blue border'></div>

CSS

.red {
    background-color: #f00;
}
.green {
    background-color: #0f0;
}
.blue {
    background-color: #00f;
}
.border {
    display: block;
    width: 3em;
    height: 3em;
    border: 10pt solid rgba(0,0,0, 0.5);
}