Untitled

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <type="text/javascript"></script>
        <script type="text/javascript" src="jquery.js"></script>
        <link rel="stylesheet" href="styles.css" type="text/css" />
        <title>Login Form</title>
        <script type="text/javascript">
            $(document).ready(function(){
                $("#login").click(function(){
                    username=$("#user_name").val();
                    password=$("#password").val();

                    $.ajax({
                        type    : "POST",
                        url     : "login.php",
                        data    : "username="+username+"&password="+password,
                        success : function(html){
                            if(html=='true'){
                                $("#add_err").html("right username And password");
                                //$("#login_form").fadeOut("normal");
                                //$("#shadow").fadeOut();
                                //$("#profile").html("<a href='logout.php' class='red' id='logout'>Logout</a>");
                            }else{
                                $("#add_err").html("Wrong username And password");
                            }
                        },
                        beforeSend:function(){
                            $("#add_err").html("Loading...")
                        }
                    });
                    return false;
                });
            });
        </script>
    </head>
    <body>
    <?php session_start(); ?>
        <div id="profile">
            <?php if(isset($_SESSION['user_name'])){ ?>

            <?php } ?>
        </div>
    </body>

    <?php if(empty($_SESSION['user_name'])){ ?>
    <div class="container" id="login_form">
        <section id="content">
            <form action="login.php">
                <h1>Login Form</h1>
                <div>
                    <input type="text" placeholder="Username" required="" id="user_name"  name="user_name"/>
                </div>
                <div>
                    <input type="password" placeholder="Password" required="" id="password"  name="password"/>
                </div>
                <div class="err" id="add_err"></div>
                <div>
                    <input type="submit" value="Log in" id="login"  />
                </div>
            </form>
            <div class="button"> </div>
        </section>
    </div>
    <?php } ?>

</html>