Switching from landscape to portrait breaks navigation on mobile

If you view the theme on a mobile device in landscape mode and open the navigation and then switch to portrait the navigation doesn't revert back to portrait mode. It only uses half of the screen space.

Start by reproducing the issue on a mobile device: open the navigation in landscape mode, rotate to portrait, and observe the available screen space. Inspect the theme's navigation and responsive styling to find why the landscape state remains after rotation. Done means the navigation uses the expected portrait layout after switching orientation.

Written by the indexing model from the issue text.