Been spending a lot of time recently in the theme editor. Love it. BUT, it’s taken me a while to work out how to rapidly get to editing the theme - until I discovered that I could publish my theme to the directory and not make it public.
With that done, you get a unique link you your personal theme.
I added the dark and light links to a draft note - tagged design.
Now as I work in drafts and find nuances I want to change - I flip to the design draft - click on one of the two links and am into the editor of the theme in a couple of seconds.
Hope this is useful to you.