You can open notebook properties from the notebook menu:
You will see its properties page:
Here you can change notebook id in order to make clean an readable urls or delete it.
You can also insert a custom footer HTML code that will be automatically added to the bottom of all notes. You can add some web stats tracking code, for example. Please note that footer content will NOT be unescaped or sanitized. Use it at your own risk.
If you want to add custom CSS or JS code to all documents of your notebook, you can either reference them from external resources or put them into the notebook itself and link it by path, name or ID. Please note that external CSS and JS files must be served from HTTPS websites or you will get a warning in your browser.
Unlike Footer, here you must provide the list of either urls or document paths/ids, one per line.