Stop accessing themes.php for subsite admin in a multisite

code.php

<?php

add_action('admin_init', 'disallowed_theme_page');
function disallowed_theme_page() {
    global $pagenow;
    if($pagenow == 'themes.php' &&  !is_super_admin()){
        wp_redirect(admin_url());
        exit;
    }
}