<html><head><script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script><script>$(document).ready(function(){ $("button").click(function(){ $("h1, h2, p").addClass("blue"); $("div").addClass("important"); });});</script><style>.important { font-weight: bold; font-size: xx-large;}.blue { color: blue;}</style></head><body><h1>Heading 1</h1><h2>Heading 2</h2><p>This is a paragraph.</p><p>This is another paragraph.</p><div>This is some important text!</div><br><button>Add classes to elements</button></body></html>