Also there's font-size party happening on the home's right sidebar. 16px, 14px, 12px in a rapid succession.

Meanwhile, on Pull Requests' right side bar everything is rendered in 12px size.

Just to be clear, 12px is equivalent of 9pt. That's fairly small on screen. For comparison the README body text is rendered in 16px, which is equivalent of 12pt.

By the way, HN body text is 13.33px, about 10pt.