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<!DOCTYPE html> <html> <title>W3.JS</title> <style> .marked { background: orange; font-size: 30px; color: white; } </style> <script src="https://www.w3schools.com/lib/w3.js"></script> <body> <p>Click the button to add the "marked" class to id="London".</p> <button onclick="w3.addClass('#London','marked')">Add Class</button> <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> </body> </html>
