Mobile menu not working #144

Steps to reproduce:

1. Open docs in mobile view
2. Click the menu at the top left

Expected result: menu opens
Actual result: menu doesn't open

• Can repro with latest https://github.com/python/python-docs-theme/releases/tag/2023.7

• Cannot repro with previous https://github.com/python/python-docs-theme/releases/tag/2023.3.1

This is due to the mobile-nav container being placed inside the document div instead of outside and before:

This is caused by #141 which moved mobile-nav, cc @miketheman.