Weird formatting issues with Galleries

I’m using the Tropicala 1.3 theme at https://www.hive101.com, and love it. My only known issue thus far (as my blog is very new) is with the WordPress Gallery option.

When setting up the Gallery, “Link images to” gives 2 options: either the image file, or an attachment page. If I set up the Gallery to use the attachment page, it takes you to a terribly formatted page when you click the image. Obviously, linking to just the image file looks fine, but doesn’t provide the same level of functionality.

Any WP gurus have an insight into how to fix this? I can find my way through PHP easily enough; I just don’t know much about deciphering the code itself to find out what’s causing this.