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<!DOCTYPE html>
<html>
<title>W3.JS</title>
<script src="https://www.w3schools.com/lib/w3.js"></script>
<body>
<p>Click the button to add a red background color to id="London".</p>
<button onclick="w3.addStyle('#London','background-color','red')">Add Style</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>
<div id="Tokyo" class="city">
  <h2>Tokyo</h2>
  <p>Tokyo is the capital of Japan.</p>
</div>
</body>
</html>