Updated theme, changed one word, broke whole site

Hello, dear helpers
I know, I know, I should have made a backup of everything before I used the ‘update theme’ button. I did not. And now I seem to have three significant issues…

1. Cloud typography is borked and I can’t see how to fix it
I thought it was all ok so I proceeded to do what I had come to do: I changed one word in a text block, and hit the Update button. But when I checked the published page, the typography was all default Times Ugly, not just for that text block, for the whole page. My cloud typography settings must have been lost? (And I can’t find now where/how I made that work in the first place.)

2. It’s no longer possible to assign a special class to a text block?
Then when I went back to look at the text block again, I noticed that the box at the bottom of the dialog box, which i had used to class the text according to a style I wrote, is no longer there, in this and all other text blocks. Did something major change in this version about how text can be styled?

I freaked out for a moment thinking that the theme update had overridden all my customisations and I’d have to recreate them from scratch. But the colours I chose, and the CSS I wrote (in the quick changes box) is all still there…

3. My home page is all but AWOL
Then I tried to revert the page to the version from yesterday, and now the whole page has gone apart from the footer.

Please advise! Thank you,
Cath