Built a 637‑line print stylesheet against four documented rendering‑engine behaviours, including run‑in headings that printed white on white for any reader whose browser preferred dark.

Situation. The site’s case studies are the artefact somebody prints and takes into a meeting. That makes paper a real output rather than a courtesy, and paper is a different medium from a narrow screen — the reader’s paper size is unknown, the reader’s orientation is unknown, and the browser’s print behaviour differs between engines in ways no screen preview reveals.

Task. The site had to print correctly on unknown paper, in both colour themes, without a separate document being maintained beside the web one.

Action. It is one 637‑line stylesheet with a single page rule and one print block. The page rule sets a margin and deliberately sets no paper size, so whatever the reader chooses in the dialog comes through and everything else adapts to it. The root font size is pinned in points so every relative measurement has a physical anchor, and one measure of about seventy‑two characters is applied to the four top‑level blocks — which is the sheet winning over the design, since a landscape page would otherwise run a line to about a hundred and ten characters. Four engine behaviours are documented as traps, each having caused a real defect. Viewport units resolve to the page box in one engine and to the window in another, so a page printed from a wide window has a third of every line cropped off in the second. Fixed‑position elements paint on every sheet, so the decorative ones are dropped and two of them are repurposed as a letterhead and a colophon. The palette defaults to white text because the default theme is dark, which printed the four section run‑in labels white on white — the words were simply absent. And paged media cannot split a flex or grid box, which produced a blank first sheet on an achievement page. A six‑part check covers it, testing six paper and orientation combinations, both colour‑scheme preferences, and the real page count against what the content height implies.

Result. The site prints on unknown paper in both themes, and the four engine behaviours are written down with the defect each produced. The known limits are recorded rather than hidden: no page numbers or running heads, one engine ignores widow and orphan control, and drop caps are not universal. A stray comment terminator once made the CSS linter swallow a whole rule and pass clean twice — only the print check noticed.