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<html><title>W3.JS</title><link rel="stylesheet" href="https://www.w3schools.com/w3css/4/w3.css"><script src="https://www.w3schools.com/lib/w3.js"></script><body class="w3-container"><h2>Testing W3.JS with CSS</h2><p>Click the button to add class='w3-red w3-xlarge' to id='London.</p><button onclick="w3.addClass('#London','w3-red w3-xlarge')">Add Classes</button><div id="London" class="w3-panel w3-border city"> <h1>London</h1> <p>London is the capital city of England.</p></div><div id="Paris" class="w3-panel w3-border city"> <h1>Paris</h1> <p>Paris is the capital of France.</p> </div><div id="Tokyo" class="w3-panel w3-border city"> <h1>Tokyo</h1> <p>Tokyo is the capital of Japan.</p></div></body></html>