Strongly relates to my previous ask from last year for account-level CSS, but this time it comes more from remembering how things used to be on MySpace and deviantArt.
Back in the late '00s, if you paid for deviantArt, you got the ability to use CSS on your journal posts. It was pretty limited, but people got really creative, and it was very fun. The CSS was stored per-journal, so previous journals wouldn't change in appearance if you changed the look of your journals (a slight drawback to this was that if you needed to change the style for everything, you'd need to change every post's CSS).
I think it'd be really neat to have something like this as a Cohost Plus! feature.
Back in the early '00s, if you had a MySpace account, you could do some frankly obscene things with your page using HTML and CSS, and people would routinely spend a long time doing exactly that, so that their page was "theirs". The idea of a user's profile page being uniquely theirs, and customisable by them, has been pretty drastically eroded over the years as social networks homogenised and became more interested in what advertisers wanted. Cohost feels like a place that doesn't need to care about this, and I feel like it'd be a good Plus! feature.
Although it's easy to do something like have a draft saved to your account with a 'default style' and you just copy-paste the code out of it, you're still stuck copy-pasting inline styles if you're writing something up. You can't really get lost in the writing without giving yourself the task of going back through what you wrote and adding styles after-the-fact.
I have already explained the motive for per-page CSS.
surprise! i don't have any this time.
Concessions / limitations
As with my suggestion for account-level site-wide CSS, I think limitations are important. Things like defining animations should probably remain out of reach. I also recognise that implementing these features may cause headaches in terms of ensuring accessibility, though i'd hope that it being a Cohost Plus! feature would reduce that somewhat.