Change markup shown before the search result
This answer has already been answered on stackoverflow. Here's a copy paste of what Cornel Andreev wrote.



You have to alter the route defined by the search module.
In order to do so:


Define in your mymodule.services.yml file following:




    services:
      mymodule.route_subscriber:
      class: Drupal\mymodule\Routing\RouteSubscriber
      tags:
        - { name: event_subscriber }




Create a class that extends the RouteSubscriberBase class on /mymodule/src/Routing/RouteSubscriber.php as following:




    /**
     * @file
     * Contains \Drupal\mymodule\Routing\RouteSubscriber.
     */

    namespace Drupal\mymodule\Routing;

    use Drupal\Core\Routing\RouteSubscriberBase;
    use Symfony\Component\Routing\RouteCollection;

    /**
     * Listens to the dynamic route events.
     */
    class RouteSubscriber extends RouteSubscriberBase {

      /**
       * {@inheritdoc}
       */
      public function alterRoutes(RouteCollection $collection) {
        // Replace dynamically created "search.view_node_search" route's Controller
        // with our own.
        if ($route = $collection->get('search.view_node_search')) {
          $route->setDefault('_controller', '\Drupal\mymodule\Controller\MyModuleSearchController::view');
        }
      }
    }




Finally, the controller itself located on /mymodule/src/Controller/MyModuleSearchController.php




    namespace Drupal\mymodule\Controller;

    use Drupal\search\SearchPageInterface;
    use Symfony\Component\HttpFoundation\Request;
    use Drupal\search\Controller\SearchController;

    /**
     * Override the Route controller for search.
     */
    class MyModuleSearchController extends SearchController {

      /**
       * {@inheritdoc}
       */
      public function view(Request $request, SearchPageInterface $entity) {
        $build = parent::view($request, $entity);
        // Unset the Result title.
        if (isset($build['search_results_title'])) {
          unset($build['search_results_title']);
        }

        return $build;
      }

    }