Problem
Ids like about, download, documentation and community in the
documentation top menu collide with the same ids inside documents
(e.g. section anchors), breaking W3C validation and <label for=...>
associations.
This is the same issue fixed for the website header in 10633eb
(D59857).
Changes
In documentation/themes/beastie/layouts/_partials/site-header.html
and trademarks.html prefix the checkbox ids and their <label for=...>
attributes with "header-", matching the fix already applied to
the website header (e.g. header-community-title).