How to replicate Image Server-generated admin view in a theme?

I would like to create a site with a small collection of public-domain maps that would enable the viewer to zoom in on visual details in the maps. After experimenting with Image Server, IIIF Server, Universal Viewer, and other viewers, which are more elaborate than I need, I realized that I could get the visual effect I’m seeking with Image Server alone. With Image Server active, the way that the media file is displayed when I go to /admin/media/{item number} is more or less exactly how I want the media to look in the theme, in particular with the zoom controls showing:

map-image

My question is: what do I need to edit in a theme in order to produce more or less the same visual effect (a window showing the media file with zoom controls) in an item’s public view? I would like to base my site’s theme on Center Row but I’d be happy to learn of a solution that would work for any other theme.