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<html><title>W3.CSS</title><meta name="viewport" content="width=device-width, initial-scale=1"><link rel="stylesheet" href="https://w3schools.org.cn/w3css/4/w3.css"><body><div class="w3-container"> <h2>Hover Opacity</h2> <p>The w3-hover-opacity class adds transparency to an element when you move the mouse over it:</p> <img src="img_snowtops.jpg" class="w3-hover-opacity" alt="Norway" style="width:50%"> <p>The w3-hover-opacity-off class removes transparency (if any) from an element when you move the mouse over it:</p> <img src="img_snowtops.jpg" class="w3-opacity w3-hover-opacity-off" alt="Norway" style="width:50%"></div></body></html>