JSFiddle - React, Tailwind, and code Playground

HTML

<span class="hr"></span>

CSS

body {
    background: mediumSeaGreen;
}

.hr {
    background: rgba(0, 0, 0, 0.6);
    height: 1px;
    width: 100%;
    display: block;
    border-bottom: 1px solid rgba(255, 255, 255, 0.6);
}