index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
    <link rel="stylesheet" href="app/styles.css">
    <link href="https://fonts.googleapis.com/css?family=Montserrat:400,500,700&display=swap" rel="stylesheet">
    <title>Digital clock</title>
</head>
<body>
    <div class="container">
        <div class="row">
            <div class="col-md-12">
                <div class="clock"></div>
            </div>
        </div>
    </div>

<script src="app/scripts.js"></script>
</body>
</html>