Dark mode: the slate scheme set the header to #3f6b3e, a dark green on a dark page, so
the bar disappeared into the background. It is now green-mid with near-black text.
Typography moves to publishing/typography.css, loaded after brand.css, and declares
Figtree on the elements themselves -- Material defines --md-text-font-family on <body>,
so a :root value loses to it by DOM proximity. Heading colours are scoped to the light
scheme, since ink is unreadable on the dark one.
