I really like the new joinmastodon page!
My only concern is that I found it a bit difficult to read due to the low contrast between the background and the non-bolded characters. Where they're bold it's easier but where they're not bold the contrast is pretty low. I have fairly decent eyesight (I have glasses but otherwise good) and I still found it difficult.
This could also be an accessibility issue. I just ran the page through the WAVE tester and it said the contrast problem would fail accessibility AA testing. http://wave.webaim.org/
I realize this isn't a legal issue (i.e., I don't think legally it has to comply), but it is a moral issue in terms of making sure the page is viewable by all!