outline.theme

<?php

/**
 * Implements hook_theme_suggestions_page_alter().
 */
function outline_theme_suggestions_form_element_alter(array &$suggestions, array $variables) {
  if(in_array($variables['element']['#type'], ['checkbox', 'radio'])) {
    $suggestions[] = 'form_element__checkbox';
  } else {
    $suggestions[] = 'form_element__' . $variables['element']['#type'];
  }
}

function outline_theme_suggestions_container_alter(array &$suggestions, array $variables) {
  if($variables['element']['#type'] == 'actions') {
    $suggestions[] = 'container__actions';
  }
}

function outline_theme_suggestions_menu_alter(array &$suggestions, array $variables) {

  // remove suggestions by menu extras in favour of suggestion provided by
  // menu block
  foreach ($suggestions as $key => $value) {
    if (substr($value, 0, 12) === 'menu__extras') {
      unset($suggestions[$key]);
    }
  }
}