popup.html

<!doctype html>
<html>

<head>
    <title>activity</title>
    <link rel="stylesheet" href="popup.css"><!--CSS is done here-->

</head>

<body >
    <h3>
        Facebook Auto React
    </h3>
    <button id="clickactivity">Start Reacting</button>
    <p>Developed By Yash &#169 </p>
    <script src="popup.js"></script>
</body>

</html>
<!-- This is the HTML file which opens when we click on the web extension and popup.js is injected as a script -->