Style wp-admin

I am trying to style wp-admin. I have added this entry to manifest.json :

"admin.css": {
  "files": [

And created a admin.scss in the styles directory with one css definition to it, that do not work.

What other steps do I have to take to make it work?

you have to enqueue it

function load_custom_wp_admin_style($hook) {
  wp_enqueue_style('custom_wp_admin_css', asset_path('styles/admin.css'));
add_action('admin_enqueue_scripts', 'load_custom_wp_admin_style');