Vellum.

Drafter’s design language. The site is a drawing: paper ground, ink type and linework, and one orange used the way an engineer uses it, as the redline.

Principles.

The page is a sheet.
Square corners, hairline rules, zone marks on the edge and a title block at the foot. A page is laid out the way a drawing is, so it reads as one document from nav to footer.
One redline.
Orange is markup, used the way a checker uses a red pen: the primary action, a link, the one thing on a visual that matters. Everything else is ink on paper.
Two typefaces.
Switzer sets what is read; IBM Plex Mono sets what annotates it. Mono uppercase is kept for labels, so it never has to compete with a sentence.
Two stocks.
A dark page is the same drawing printed as a negative. One class swaps every token's value, and nothing else on the page changes.
Pictures are prepared.
Each picture is treated for the stock it lands on: dithered, toned, or framed on vellum. None arrives as a white rectangle on paper.
A known running order.
Every kind of page has its shape, and every section beside some words is one of three containers. A new page keeps its template's order and gets its own words.