Load specific slide in 7.1 gallery

Hello,

I've built a fullscreen overlay for my gallery that will hold thumbnails of the gallery content images.

The idea is that, on thumbnail click, the specific corresponding large image slide will load behind the overlay. I see that Squarespace treats these slides as list items;

is it possible to target/call specific slides, and is it possible to do this without JS please?

Any help here would be very much appreciated.

Many thanks.