You can try add this into your functions.php
// Custom Admin Style
function admin_style() {
wp_register_style( 'admin_style', get_stylesheet_directory_uri() . '/css/admin.css' );
wp_enqueue_style( 'admin_style' );
}
add_action( 'admin_enqueue_scripts', 'admin_style' );
Replace get_stylesheet_directory_uri() using get_template_directory_uri() if your site not running via child theme.
You’ll also need to create a stylesheet in the /css directory in your themes folder.. let say admin.css and put this code https://pastebin.com/b2PyDqLC and the result https://pbrd.co/1eaHWJ0
