modules/custom/d_product/src/Plugin/Block/MobileFilters.php
public function blockSubmit($form, FormStateInterface $formState) {
    $this->configuration['button_text'] = $formState->getValue('button_text');
    $this->configuration['button_class'] = $formState->getValue('button_class');
  }
public function blockSubmit($form, FormStateInterface $formState) {
    $this->configuration['button_text'] = $formState->getValue('button_text');
    $this->configuration['button_class'] = $formState->getValue('button_class');
  }
{@inheritdoc}