Class Elements

<!DOCTYPE html>
<html>
<head>
<style>
.mystyle {
  width: 300px;
  height: 50px;
  background-color: coral;
  color: white;
  font-size: 25px;
}

.newClassName {
  width: 400px;
  height: 100px;
  background-color: lightblue;
  text-align: center;
  font-size: 25px;
  color: navy;
  margin-bottom: 10px;
}
</style>
</head>
<body>

<p>Click the button to toggle between two classes.</p>

<button onclick="myFunction()">Try it</button>

<p><strong>Note:</strong> The classList property is not supported in Internet Explorer 9 and earlier versions.</p>

<div id="myDIV" class="mystyle">
I am a DIV element
</div>

<script>
function myFunction() {
  document.getElementById("myDIV").classList.toggle("newClassName");
}
</script>

</body>
</html>