get_stylesheet_directory_uri() is a PHP function, you must use it in a PHP file instead of your CSS file.
In your functions.php you can paste this code and change depends on your needs:
function my_login_logo() { ?>
<style type="text/css">
body.login div#login h1 a {
background-image: url(<?php echo get_stylesheet_directory_uri(); ?>/images/Logo-B-Classic.jpg);
}
</style>
<?php }
add_action( 'login_enqueue_scripts', 'my_login_logo' );