Untitled

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .paused {
          background: #ddd;
          color: #555;
        }
    </style>
</head>
<body>
    <p id="log">Click on this document to give it focus.</p>
    <script>
        function pause() {
          document.body.classList.add("paused");
          log.textContent = "FOCUS LOST!";
        }

        function play() {
          document.body.classList.remove("paused");
          log.textContent =
            "This document has focus. Click outside the document to lose focus.";
        }

        let log = document.getElementById("log");

        window.addEventListener("blur", pause);
        window.addEventListener("focus", play);

    </script>
</body>
</html>