Mac – Setting default Emacs window margins

I'm trying to emulate some behavior of the darkroom-mode Emacs mode — specifically the margins setup.

I've figured out one piece of the puzzle — specifically, to change window margins, I can eval (set-window-margins nil <left margin> <right margin>).

Which is fine, but I'm noticing that the changes only occur in the current window, and will actually go back to the default margin if I switch to a different buffer using C-x left or right arrow key.

I'd like to figure out how to do the following:

• Set it so that all buffers get the same window-margin settings.
• Set it so that the margin settings persist after changing windows.

I know that it might involve using hooks, but I'm not exactly sure which hooks to use.