What did Einstein's unified theory look like, quantitatively?

I’m writing an essay on the history of physics from a mathematical point of view. It’s divided into a handful of impactful persons/ideas, one of the largest being the works of Einstein. Immediately following Einstein is a discussion of more ‘modern’ work on unified theories. I’d like to include some information, as substantial as possible (i.e. the essay focuses primarily on presenting ideas, in the raw, themselves, supported by a touch of historical context), on Einstein’s work on this problem. Unfortunately, however, I’m unable to find much outside of some purely quantitative historical anecdotes.

So, what did Einstein’s unified theory look like, on paper? Obviously, it was left unfinished (and, some might argue is an impossible task), however surely we know something about the direction(s) he took, what the mathematical framework looked like, etc. Perhaps even just some inklings?