How can I make photos open in a "lightbox"?

I followed these directions to make photos on Item pages open in a lightbox.

https://omeka.org/classic/docs/Technical/Adding_LightBox_to_Omeka/

The solution worked, but it depends upon making “sure that the Item File Gallery option is checked.” And that option puts the photos on the Item page in a grid of thumbnails, which I don’t want. Here’s my site, using the Emiglio theme:

https://topangahistoricalsociety.org/archive/document/1257