how to block css from external access

Generate your css with PHP like style.css.php and in the code accept a token which refreshes every second. Your main page will include it using the current token src="style.css.php?token=abc123". If the token is valid, it serves it up. If the token is expired, it doesn't.

Dumbest solution ever. Endless workarounds, but might help against that guy who wants to steal your CSS. Worth a try and a good laugh.

Step 1: Create a table css_security_force in your database with one column token

Step 2: Create a cron that runs every second to update the token (now THAT's secure):

UPDATE css_security_force SET token = md5( NOW() );

Step 3: In your PHP head grab the token from the css_security_force table and set it as a variable $token then reference that token in the CSS link:

<link rel="stylesheet" href="style.css.php?token=<?=$token?>" />

Step 4: In your style.css.php file, grab the token from the database and check it against the query param.

if ($_GET['token'] == $token) {
    echo <<<CSS
        body {
            background-color : yellow;
            color : pink;
        }
CSS;
} else {
    echo 'Stop stealing my CSS!!!!!!';
}

Sit back and watch your foe's plans crumble before him.

EDIT I got curious and made a working demo (Took it down after a couple days of 1 second db updates for sanity purposes, but you can easily recreate with the source posted below).

Here is the source on Github

No. This makes no sense. Your CSS file must be available to anyone who can view your site if you want your pages styled.

Who cares if someone uses your style?

Simply put you cannot block it because the browsers have to have access to them. It is just one of those things you should not worry about. If it were possible, many sites like Facebook and Twitter would be blocking it.