<style>
.first-class { background-color: yellow; }
.second-class { border: 2px dashed blue; }
.third-class { display: none; }
.fourth-class { font-size: 14px; }
</style>
<div id="myDiv">Multiple class handling</div>
<script>
document.getElementById("myDiv").classList.add("first-class", "second-class");
document.getElementById("myDiv").classList.remove("third-class", "fourth-class");
</script>