index.html

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title>YouTube Background Player</title>
    <style>
        html,
        body,
        webview {
            width: 100%;
            height: 100%;
            padding: 0px;
            margin: 0px;
        }
    </style>
</head>

<script>
</script>

<body>
    <!-- Intentionally using Chrome 42. That is because Chrome 55 will stop video if the window is blured. -->
    <webview id="video" preload="./preload.js" src="about:blank" useragent="Mozilla/5.0 (Linux; Android 7.1.1;) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2307.2 Mobile Safari/537.36"></webview>
</body>

<script src="./script.js"></script>

</html>