HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>fadeTo basic dim</title>
  <style>
    body { font-family: sans-serif; padding: 16px; max-width: 28rem; }
    #book { padding: 16px; background: #fef3c7; border: 2px solid #d97706; border-radius: 8px; margin-top: 12px; }
    #clickme { color: #2563eb; cursor: pointer; text-decoration: underline; }
  </style>
</head>
<body>
  <span id="clickme">Click here</span>
  <div id="book">This box dims to 50% opacity — it stays visible in layout.</div>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <script>
    $("#clickme").on("click", function () {
      $("#book").fadeTo("slow", 0.5, function () {
        console.log("Animation complete.");
      });
    });
  </script>
</body>
</html>

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jQuery .fadeTo() — dim to 50% opacity (Try It)