index.html

<html>
<head>
    <title>DPaint JS</title>
    <meta name="viewport" content="width=device-width, initial-scale=1,maximum-scale=1, user-scalable=no" />
    <link rel="manifest" href="manifest.json">
    <meta name="mobile-web-app-capable" content="yes">
    <meta name="theme-color" content="#282A2C">
    <link rel="stylesheet" href="_style/main.css">
    <script type="module" src="_script/app.js"></script>
</head>
<body>

<script>
    if (window.location.protocol==="file:"){
        document.body.innerHTML = "<h1 class='error'>You have opened index.html from your file system. This won't work, please serve this file from a (local) webserver.<br><br><a href='https://www.stef.be/dpaint/docs/'>Documentation</a></h1";
    }
</script>

</body>
</html>