Easy Password Protected Page with Persistent Login

<?php
    // The master password.
    $password = "pass";

    // Used to get the filename
    $u = explode('/', $_SERVER["SCRIPT_NAME"]);
    $script = $u[count($u) - 1];

    // Used to tell if the user is logged in and whether or not they wish to logout.
    session_start();
    if(isset($_POST["password"]) && ($_POST["password"] == $password)) $_SESSION["authed"] = true;
    if(isset($_GET["action"]) && ($_GET["action"] == "logout")) { $_SESSION["authed"] = false; header("Location: " . $script); }
    if(!$_SESSION["authed"]):
?>
<!DOCTYPE html>
<html>
    <head>
        <title>Login</title>
        <style type="text/css">
            *{margin:0;padding:0}html,body{height:100%;background-color:#eaeaea;font-family:Tahoma,Geneva,sans-serif;color:#333}input{border:1px solid #aaa;border-radius:4px;padding:4px;color:#aaa;width:192px}input:hover{border:1px solid #777;color:#333}input:focus{color:#333;outline:0;border:1px solid #5096e1;-webkit-box-shadow:0 0 4px rgba(80,150,225,0.5);-moz-box-shadow:0 0 4px rgba(80,150,225,0.5);box-shadow:0 0 4px rgba(80,150,225,0.5)}input[type="submit"]{width:200px;background-color:#fff}input[type="submit"]:active{-webkit-box-shadow:0 0 6px rgba(50,50,50,0.35);-moz-box-shadow:0 0 6px rgba(50,50,50,0.35);box-shadow:0 0 6px rgba(50,50,50,0.35)}.wrapper{height:100%;display:table;margin:0 auto;vertical-align:middle}.contentwrapper{display:table-cell;vertical-align:middle}.content{position:relative;border:1px solid #aaa;-webkit-border-radius:8px;-moz-border-radius:8px;border-radius:8px;background-color:#fff;padding:20px;margin-top:14px;-webkit-box-shadow:0 0 20px rgba(50,50,50,0.35);-moz-box-shadow:0 0 20px rgba(50,50,50,0.35);box-shadow:0 0 20px rgba(50,50,50,0.35)}.header{position:absolute;width:96px;height:20px;top:-15px;left:50%;padding:4px;margin-left:-51px;text-align:center;background-color:#fff;border:1px solid #aaa;-webkit-border-radius:32px;-moz-border-radius:32px;border-radius:32px -webkit-box-shadow:0 0 2px rgba(50,50,50,0.35);-moz-box-shadow:0 0 2px rgba(50,50,50,0.35);box-shadow:0 0 2px rgba(50,50,50,0.35)}.section{margin-top:8px;text-align:center}.error,.success{margin-top:0;color:red;font-size:13px;max-width:200px}.success{color:green}
        </style>

        <!--[if lt IE 9]>
            <script src="http://html5shim.googlecode.com/svn/trunk/html5.js"></script>
        <![endif]-->
    </head>
    <body onload="document.getElementById('password').focus()">
        <div class="wrapper">
            <div class="contentwrapper">
                <div class="content">
                    <div class="header">Login</div>
                    <form action="<?=$script?>" method="post">
                        <div class="section"><input type="password" name="password" id="password" placeholder="Password"></div>
                        <div class="section"><input type="submit" value="Login"></div>
                    </form>
                </div>
            </div>
        </div>
    </body>
</html>
<?php else: ?>

<!-- Your hidden content -->
<!DOCTYPE html>
<html>
    <head>
        <title>Title</title>
    </head>
    <body>
        <p>Content!</p>

        <!-- If you want to let the user logout, simply direct them to '?action=logout' with $script like so: -->
        <a href="<?=$script?>?action=logout"><input type="button" value="Logout"></a>
    </body>
</html>
<!-- End of your hidden content -->

<?php endif; ?>