Untitled

<?php
include("checklogin.php");
include("server.php");

if(isset($_POST['submit']))
{
    $username = $_POST['username'];
    $password = ($_POST['password']);

    $check_user = "SELECT * FROM manager WHERE username='$username' AND password='$password'";
    $run = mysql_query($check_user);


    $username = mysql_result($run,0,'username');
    $level = mysql_result($run,0,'level');

    if($level == 'stuff')
    {
        if(mysql_num_rows($run)>0)//user exisi in db
        {
        $_SESSION['username']=$username;

        echo "<script>window.open('stuff.php','_SELF')</script>";
        }//end numrows

        }//end level admin

        else if($level == 'manager')
            {
            if(mysql_num_rows($run)>0)
            {
            $_SESSION['username']=$username;

            echo "<script>window.open('homepage.php','_SELF')</script>";
            }
            }//end lvl manager

            else if($level == 'student')
            {
            if(mysql_num_rows($run)>0)
            {
            $_SESSION['username']=$username;

            echo "<script>window.open('student.php','_SELF')</script>";
            }
            }//end lvl student

        else
            {
            echo "<script>alert('Username or Password is incorrect!')</script>";
            }
}
?>
<!DOCTYPE html>
<html>
<head>
    <title>Admin Login</title>
    <style type="text/css">
body {
    background-image:url(assets/img/background.JPG);
    background-repeat:no-repeat;
    background-size:cover;
}
.aa{
    width: 500px;
    height: 300px;
    background-color: rgba(0,0,0,0.5);
    margin:0 auto;
    margin-top:40px;
    padding-top: 10px;
    padding-left: 50px;
    border-radius: 15px;
    -wekbit-border-radius: 15px;
    -o-border-radius:15px;
    -moz-border-radius:15px;
    color:white;
    font-weight:bolder;
}
.aa input[type="id"]{
    width: 250px;
    height: 35px;
    border: 5px;
    margin: 0 auto;
    padding: 10px;
    border-radius: 10px;
}
.aa input[type="password"]{
    width: 250px;
    height: 35px;
    border: 5px;
    margin: 0 auto;
    padding: 10px;
    border-radius: 10px;
}
.aa input[type="submit"]{
    width: 100px;
    height: 35px;
    border: 5px;
    border-radius: 10px;
    text-align:center;
    background-color:skyblue;
    </style>

</head>
<body>

<div class="aa"
<h2>Login</h2><br>
<br/>
<form name="form1" method="POST" action="<?php echo htmlspecialchars($_SERVER ['PHP_SELF']);?>">
  <td> Username: </td>
    <input name="username" type="id" id="username" placeholder="Please Enter Username...." required="required"><br>
    </br>
    <td> Password: </td>
    <input name="password" type="password" id="password" placeholder="Plese Enter Password....." required="required"><br>
    <br/>

    <center><input type="submit" name="submit" value="Login"></center>

</form>

</div>
</body>
</html>