Avoid adding custom CSS to a node editing form?

Question

Situation

• custom module adding styles
• don't add styles to node editing form

How to avoid adding the style to the editing forms?

function crossfade_page_attachments(array &$page) {
  $page['#attached']['library'][] = 'crossfade/crossfade';
}

Answer 1

Currently discovered answer derived from the metatag module)

function crossfade_page_attachments(array &$page) {
  if (\Drupal::service('router.admin_context')->isAdminRoute()) {
    return FALSE;
  }
  $page['#attached']['library'][] = 'crossfade/crossfade';
}