Drupal 8 - Adding Twig Template Suggestions for block Elements

In this article, I'll show you how to add Twig Template Suggestions for block Elements in drupal 8 with hook_theme_suggestions_block_alter():

/**
 * Implements hook__suggestions_HOOK_alter().
 */
function THEMENAME_theme_suggestions_block_alter(array &$suggestions, array $variables)
{
    if (!empty($variables['elements']['#id'])) {
        $block = Drupal\block\Entity\Block::load($variables['elements']['#id']);
        $suggestions[] = 'block__' . $block->getRegion();
        $suggestions[] = 'block__' . $block->getRegion() . '__' . $variables['elements']['#id'];
    } elseif (!empty($element['content']['#block_content'])) {
        $block_bundle = $element['content']['#block_content']->bundle();
        $suggestions[] = 'block__' . $block_bundle;
    }
    return $suggestions;
}