/**
 * Implements hook_css_alter().
 */
function {{ machine_name }}_css_alter(&$css, \Drupal\Core\Asset\AttachedAssetsInterface $assets) {
  // Remove defaults.css file.
  $file_path = \Drupal::service('extension.list.module')->getPath('system') . '/defaults.css';
  unset($css[$file_path]);
}