JSFiddle - React, Tailwind, and code Playground
HTML
<pre id="code">
this is a test
</pre>
CSS
.keyword{color:red;}
JavaScript
var keywords = ['this','test'];
var codeBlock = document.getElementById('code');
for (var j = 0; j < keywords.length; j++)
{
codeBlock.innerHTML = codeBlock.innerHTML.replace(new RegExp(keywords[j], "g"), "<span class=\"keyword\">" + keywords[j] + "</span>");
}