For deeply nested posts, you have to click on the "X minutes ago" header to get the reply option to show up.
It looks like when I add the angle brackets that CommonMark allows to circumvent the spaces thing, some variations still don't work: https://i.imgur.com/nqiQnl3.png
For one more note, the obsidian.css thing for styling is deeply unintuitive, because you can't edit it from inside the app: if you make a note named "obsidian.css" at the root level, that gets ignored because it's actually obsidian.css.md, so you can only edit the styling with a separate app altogether to create/edit that file directly.
It looks like when I add the angle brackets that CommonMark allows to circumvent the spaces thing, some variations still don't work: https://i.imgur.com/nqiQnl3.png
For one more note, the obsidian.css thing for styling is deeply unintuitive, because you can't edit it from inside the app: if you make a note named "obsidian.css" at the root level, that gets ignored because it's actually obsidian.css.md, so you can only edit the styling with a separate app altogether to create/edit that file directly.