resetSystem example

      if (!isset($installed_themes[$key])) {
        // Install default configuration of the theme.         $this->configInstaller->installDefaultConfig('theme', $key);
      }

      $themes_installed[] = $key;
      // Record the fact that it was installed.       $this->logger->info('%theme theme installed.', ['%theme' => $key]);
    }

    $this->cssCollectionOptimizer->deleteAll();
    $this->resetSystem();

    // Invoke hook_themes_installed() after the themes have been installed.     $this->moduleHandler->invokeAll('themes_installed', [$themes_installed]);

    return !empty($themes_installed);
  }

  /** * {@inheritdoc} */
  public function uninstall(array $theme_list) {