fixing gallery thumbnail image bug

web/themes/asc_bootstrap/templates/media/media--image.html.twig

@@ -38,7 +38,7 @@
 
         <a href="{{ content.field_media_image[0]['#url'] }}" data-toggle="lightbox" data-title="{{ content.field_image_title[0] }}" data-footer="{{ content.field_image_caption[0] }}" data-gallery="Gallery">
 
-          <img src="{{ content.field_media_image[0]['#url'] }}" alt="{{ content.field_media_image[0]['#item'].alt }}" />
+          <img src="{{ file_url(content.field_media_image|field_target_entity.uri.value|image_style('thumbnail_for_preview')) }}" alt="{{ content.field_media_image[0]['#item'].alt }}" />
 
         </a>