Content cut off when printing to PDF (wrong page format?)

When printing http://dougengelbart.org/content/view/138 to a PDF in Chromium, it looks like you'd expect:

When doing the same with QtWebEngine via the html2pdf example, the page format seems to be wrong:

(Apologies if this is a duplicate - I remember various other issues related to margins and page formats when printing, but all I found were fixed)