All your changes are automatically saved while you work.
To close the file, simply close the browser tab with the application.
Before closing, it is recommended to make sure that all changes are saved. You should see the message "All changes are saved" in the status bar (at the bottom of the window).
Possible errors
If the application fails to save changes, a warning will appear at the top of the window. It does not block operation.
It is recommended to copy all contents to a new file to avoid losing data.