JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title></title>
  <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<style>
  *{margin:0;padding:0;font-size:15px;font-family:helvetica,arial,sans-serif}
  footer,section,header{display:block;}
</style>
</head>
<body>
  <header><h1></h1></header>
  <section>
  <div class="catchadream"></div>
  </section>
  <footer>
  <p id="temp">Written by 
    <a href="http://wait-till-i.com/">Chris Heilmann</a> - 
    <a href="http://twitter.com/codepo8">@codepo8</a>
  </p>
</footer>
</body>
</html>

CSS

.myclass {color:red;}

JavaScript

var p = getElementById("temp");
p.setAttribute("class", "myclass");