custom css in admin panel by user id

Use below code into functions.php file. Make sure you are using it right way
use admin_enqueue_scripts

add_action('admin_enqueue_scripts', 'FUNCTION_NAME');function FUNCTION_NAME() {
 global $current_user;
 $user_id = get_current_user_id();
 if(is_admin() && $user_id == '2'){
    wp_enqueue_style( 'admin_css', get_template_directory_uri() . '/admin-style.css', false, '1.0.0' );
}}