index.html

<!DOCTYPE html>
<html lang="en">
    <head>
        <title>TODO List</title>
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <link href="https://fonts.googleapis.com/css?family=Dancing+Script:400,700|Duru+Sans&display=swap" rel="stylesheet">
        <link rel="stylesheet" href="style.css">
        <script>
            if(/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent) || screen.width <= 699){
                document.location = "mobile.html";
            }
        </script>
    </head>
    <body>
        <header>
            <h1>Todo List</h1>
        </header>
        <form id="task-form" onsubmit="return false">
            <div class="text-area" id="task-input" contenteditable="true"></div>
        </form>        

        <ul class="task-list" id="task-list">
        </ul>       
        <script type="text/javascript" src="app.js"></script> 
    </body>
</html>