[m24] Navigation styling breaks when old nav CSS is removed from base bundle

[alexgibson]

Description

The CSS for the new navigation is overriding the stylesheet for the older navigation, so when we remove the old styles the new styles break:

Steps to reproduce

Comment out these two lines: https://github.com/mozilla/bedrock/blob/main/media/css/protocol/protocol-mozilla-2024.scss#L32-L33

Expected result

Both the new navigation and footer should display as expected.

Actual result

The footer seems OK, but the new navigation breaks since it relies on existing styles in the old navigation stylesheet.

Environment

N/A