Drupal 8 - Block Attributes

Block Attributes.php

  /**
   * {@inheritdoc}
   */
  public function build() {
    return [
      '#theme' => 'cfc_footer_block',
      '#attributes' => [
        'class' => ['footer'],
      ],
      '#cache' => [
        'max-age' => Cache::PERMANENT,
      ],
    ];
  }