Untitled

<!DOCTYPE html>
<html>
<head>
    <style>
        #bulb {
            width: 100px;
            height: 100px;
            background-color: gray;
            border-radius: 50%;
        }
    </style>
</head>
<body>
    <div id="bulb"></div>

    <button onclick="turnOnOff()">Turn On/Off</button>

    <script>
        let isOn = false;

        function turnOnOff() {
            const bulb = document.getElementById('bulb');
            if (isOn) {
                bulb.style.backgroundColor = 'gray';
            } else {
                bulb.style.backgroundColor = 'yellow';
            }
            isOn = !isOn;
        }
    </script>
</body>
</html>
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