How does Ghost Alto relate to Github Alto?

I’m trying to make modifications to the Alto theme, and I’m hoping to do those in a git repository in order to make it easier to pull in upstream updates.

That said, when I look at the version of Alto that I get from selecting the Alto theme on the “Change Theme” page in settings, and then doing “download,” it doesn’t seem to map to any of the tags within the Alto github project (and in particular, it doesn’t match v1.0.0, even though the listed version in the Ghost UI is v1.0.0).

So where should I be looking to get the baseline version of Alto that is offered by the Ghost UI?

As far as I’m aware, the themes page downloads from the GitHub main branch