Provide style guide and minimal output template for other sites

Once the nav redesign is implemented, we need a developer's guide to the minimal styling/output template needed so that a handful of othersite.apache.org domains can use to update their styling to mirror or match the main a.o site.

For example, some Whimsy pages provide custom categorized/organized content about board meeting minutes, which are useful for the general public:

https://whimsy.apache.org/board/minutes/

Since that page has a useful structured & automated output of data that's focused on the general public, the Whimsy PMC would like to match or even just "mostly mirror" the main a.o site's style, without needing to directly be part of the main site's build system. There are likely other similar sites that would like to do the same things.

Start by reviewing the main site's nav redesign and the Whimsy board minutes page to identify the styling and output patterns that should be shared. Document the minimal styling/output template and explain how other othersite.apache.org domains can use it without joining the main site's build system; done means those sites have a practical guide for mostly mirroring the main style.

Written by the indexing model from the issue text.