Cannot enlarge thumbnail

Hi! You need to override some CSS classes in your theme. See https://git.drupalcode.org/project/media_gallery/-/blob/2.0.x/css/media_...

Thanks for your response.
I'm afraid I don't quite follow what you mean, could you elaborate?

Your site has theme. You need to override some CSS classes in your theme. You can ask about it in Slack or Drupal forums (I mean how to edit CSS). This is not media gallery problem