index.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>GitHub API</title>
    <link rel="icon" type="image/png" href="assets/favicon.png">

    <!-- Import the Bootstrap CSS CDN -->
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">

</head>

<body>

    <h3 class="text-center mt-5">GitHub API</h3>
    <form id="gitHubForm" class="form-inline mx-auto" style="width: 280px">
        <input id="usernameInput" class="form-control mb-5" type="text" name="username" placeholder="GitHub Username">
        <input type="submit" class="btn btn-primary ml-2 mb-5" value="Submit">
    </form>
    <ul id="userRepos" class="list-group mx-auto mb-5" style="width: 500px">

    </ul>

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

</html>