index.html

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>Page Title</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" type="text/css" media="screen" href="main.css" />
    <script src="main.js"></script>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
</head>
<body>
    <div class="container">
        <div class="row">
            <div class="col-md-6 col-md-offset-3">
                <div class="panel panel-default" style="margin-top: 10em;">
                    <div class="panel-heading">Login</div>
                    <div class="panel-body" style="padding: 1em;">
                        <form class="form-horizontal" method="POST" action="php/login.php">
                            <div class="form-group">
                                <label for="username" class="col-md-4 control-label">Username</label>
                                <div class="col-md-6">
                                    <input id="email" type="text" class="form-control" name="username" placeholder="Username" required autofocus>
                                </div>
                            </div>

                            <div class="form-group">
                                <label for="password" class="col-md-4 control-label">Password</label>

                                <div class="col-md-6">
                                    <input id="password" type="password" class="form-control" placeholder="Password" name="password" required>
                                </div>
                            </div>
                            <div class="form-group">
                                <div class="col-md-12">
                                    <button type="submit" class="btn btn-primary" style="width:100%;">
                                        Login
                                    </button>
                                </div>
                            </div>
                        </form>
                    </div>
                </div>
            </div>
        </div>
    </div>
</body>
</html>