custom admin style on multisite wordpress

Question

I'm trying to call custom file in network admin:

function admin_css_function(){
   wp_enqueue_style('blaa', '/wp-content/themes/theme-name/assets/css/admin/admin.css', false);
}

if (is_admin()) {
  add_action('admin_enqueue_scripts', 'admin_css_function');
}

or

if (is_network_admin()) {
  add_action('admin_enqueue_scripts', 'admin_css_function');
}

But it doesn't work. This example css loads only in a single admin site from the network, but not on the network admin.

Thanks for help,