Is there some kind of sync mechanism? I couldn't see anything about account creation. You say "offline first". Is it not "offline only"?
Sync may well be coming, but I'm not yet certain how to do it securely. That being said, import & export is available now, so it can be manually sync'd.
it would be cool to have some export or import button to save everything into some kind of archive, then you can move it between offline machines and import it into the browser to use it there.