<!DOCTYPE html>
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<style>
body, html {
    font-family: -apple-system;
    font-size: 1em;
    width: 100%;
    height: 100%;
}
</style>
<body contenteditable></body>
<script>
document.body.focus();
</script>