Untitled

<!DOCTYPE html>
<html>
  <head>
    <meta name="description" content="Imperative Programming">
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title></title>
  <style id="jsbin-css">
.red {
  background-color: red
}
</style>
</head>
  <body>
    Imperative Programming<br/>
    <button id='btn'>Click Me</button>
    <div class='clicked'>I have been clicked</div>
  <script id="jsbin-javascript">
/*jshint esnext: true */
let b = document.querySelector('#btn');
b.addEventListener('click', function(){
  let clicked = document.querySelector('.clicked');
  console.log(clicked);
  clicked.classList.add('red');
});
</script>


<script id="jsbin-source-css" type="text/css">.red {
  background-color: red
}</script>

<script id="jsbin-source-javascript" type="text/javascript">/*jshint esnext: true */
let b = document.querySelector('#btn');
b.addEventListener('click', function(){
  let clicked = document.querySelector('.clicked');
  console.log(clicked);
  clicked.classList.add('red');
});</script></body>
</html>