<html><title>W3.JS</title><style>.marked { background-color: orange; font-size: 30px; padding: 16px; color: white;}</style><script src="../lib/w3.js"></script><body><h2>Testing W3.JS in HTML</h2><p>Click the button to add the "marked" class to id="London".</p><p><button onclick="w3.addClass('#London','marked')">Add Class</button></p><div id="London" class="city"> <h2>London</h2> <p>London is the capital city of England.</p></div><div id="Paris" class="city"> <h2>Paris</h2> <p>Paris is the capital of France.</p> </div><div id="Tokyo" class="city"> <h2>Tokyo</h2> <p>Tokyo is the capital of Japan.</p></div></body></html>