JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html xmlns:test="http://localhost/">
<head>
 <style>
     test\:div { color: red } 
 </style>
</head>
<body>
   <div>Not red</div>
   <test:div>Red</test:div>
    <script>
        var node = document.getElementsByTagNameNS( "*", "test\:div" ).item(0);
        alert( node.innerHTML )
    </script>
</body>
</html>