JavaScript Tambahkan ClassName

<!DOCTYPE html>
<html>
  
<head>
    <title>JavaScript to add class name</title>
    <style>
    .addCSS {
        color: green;
        font-size: 25px;
    }
    </style>
</head>
  
<body style="text-align:center;">
    <h1 style="color:green;"> 
        GeeksforGeeks 
    </h1>
    <p id="p"> A Computer Science portal for Geeks. </p>
  
    <button onclick="addClass()"> AddClass </button>
      
    <!-- Script to add class name -->
    <script>
    function addClass() {
        var v = document.getElementById("p");
        v.className += "addCSS";
    }
    </script>
</body>
  
</html>