drupal 8 theme suggestions code example

Example 1: drupal 8 form element theme suggestions

function MYMODULE_theme_suggestions_form_element_alter(array &$suggestions, array $variables, $hook) {
  if ( $variables['element']['#id'] === 'FORMID') {
    $suggestions[] = $hook . '__custom';
  }
}

Example 2: drupal 8 suggestions

function MYMODULE_theme_suggestions_alter(array &$suggestions, array $variables, $hook) {
  if (\Drupal::currentUser()
    ->isAuthenticated() && in_array($hook, array(
    'node',
    'taxonomy_term',
  ))) {
    $suggestions[] = $hook . '__' . 'logged_in';
  }
}