<!DOCTYPE html>
<html>
<head>
<style>
.mystyle { margin: 20px; width: 300px; height: 50px; background-color: coral; color: white; font-size: 25px;
}
</style>
</head>
<body>
<p>Click the button to add the "mystyle" class to DIV.</p>
<button onclick="myFunction()">Try it</button>
<div id="myDIV">
I am a DIV element
</div>
<br>
<script>
function myFunction() { document.getElementById("myDIV").classList.add("mystyle");
}
</script>
</body>
</html>