node_form_system_themes_admin_form_submit

node_form_system_themes_admin_form_submit($form, FormStateInterface $form_state)

function node_form_system_themes_admin_form_submit($form, FormStateInterface $form_state) {
  \Drupal::configFactory()->getEditable('node.settings')
    ->set('use_admin_theme', $form_state->getValue('use_admin_theme'))
    ->save();
  \Drupal::service('router.builder')->setRebuildNeeded();
}