class TestController

class TestController extends ControllerBase {
    
    /**
     * Renders a link to open the /admin/content view in a modal dialog.
     */
    public function modal() {
        $build = [];
        $build['open_admin_content'] = [
            '#type' => 'link',
            '#title' => $this->t('Administer content'),
            '#url' => Url::fromUserInput('/admin/content'),
            '#attributes' => [
                'class' => [
                    'use-ajax',
                ],
                'data-dialog-type' => 'modal',
                'data-dialog-options' => Json::encode([
                    'dialogClass' => 'views-test-modal',
                    'height' => '50%',
                    'width' => '50%',
                    'title' => $this->t('Administer content'),
                ]),
            ],
            '#attached' => [
                'library' => [
                    'core/drupal.dialog.ajax',
                ],
            ],
        ];
        return $build;
    }

}