How to load a CSS file into WordPress admin area using Child Theme? [closed]

You need to use admin_enqueue_scripts hook to load CSS in admin area.

This goes in your themes functions.php. Assumed that your file is at child_theme_path/css/admin-css.css

function wpse239532_load_admin_style() {
    wp_enqueue_style( 'admin_css', get_stylesheet_directory_uri() . '/css/admin-css.css', false, '1.0.0' );
   }

add_action( 'admin_enqueue_scripts', 'wpse239532_load_admin_style' );