<html><head><script src="https://libs.baidu.com/jquery/2.1.4/jquery.min.js"></script><script>$(document).ready(function(){ $("button").click(function(){ $("p, h1").removeClass("head intro main"); });});</script><style>.head { font-size: 2em; color: green;}.intro { font-size: 120%; color: red;}.main { font-size: 20px; color: blue;}</style></head><body><h1 class="head">This is a heading</h1><p class="intro">This is a paragraph.</p><p class="main">This is another paragraph.</p><button>Remove the "head", "intro" and "main" class from the selected elements</button></body></html>