Copy the entire code below and paste it over the current file on Neocities (replace everything). Then the other person refreshes.
How collab works on Neocities: There is no server. When either of you changes something, click Save for Neocities.
Copy the generated HTML and paste it over the existing file on your shared Neocities site. The other person refreshes and sees the new state.
Only store password hints. Code snapshots are saved when you log activity so you can revert later.