JSFiddle - React, Tailwind, and code Playground

HTML

<html xmlns:ui="http://crystalminds.nl/ns/ui#">
<head>
    <title>User Interface</title>
</head>
<body>

    <ui:tabbar>
        User Interface Tab Bar
    </ui:tabbar>
    
    <div class="tabbar">
        User Interface Tab Bar
    </div>

</body>
</html>

CSS

tabbar
{
    display                : block;
    font-weight            : bold;
    color                : white;
    background-color    : black;
}

.tabbar
{
    display                : block;
    font-weight            : bold;
    color                : white;
    background-color    : black;
}