Drupal8 - Custom views exposed form suggestions

drupal8_views_exposed_form_theme_suggestions.php

<?php

/**
 * Implements hook_theme_suggestions_HOOK_alter().
 */
function MYTHEME_theme_suggestions_views_exposed_form_alter(array &$suggestions, array $vars) {
  // form[#id] pattern is views-exposed-form-VIEWNAME-DISPLAY
  // We need to remove the 'views-exposed-form-' part
  // and to replace underscores with dashes
  $suggestions[] = 'views_exposed_form__' . str_replace(
    ['views-exposed-form-', '-'],
    ['', '_'],
    $vars['form']['#id']);
}