Personally I find vim autocomplete to be nice with plugins like YCM or COC. I have a TabNine plugin which does eat up a ton of ram, but that is because I've disabled the networking capabilities. If you want some good autocomplete experience try some of the language servers.
I went back to the site because you seem to value input and scrolled down to where I anticipated some information to be, only to have to wait >3 seconds to see any information.
the fact that as soon as I opened the page on mobile I got 3 different boxes in the way of the text I'm trying to read. any site that does this I immediately click off of
I actually had achieved this effect (with the same setup, just replace Yabai with chunkwm) a very long time ago (before El Capitan). I just spent an hour or so searching for the particular theme I used but couldn't find it. From what I remember, you can use a tool like https://github.com/insidegui/AssetCatalogTinkerer to change the System Appearance.