I suspect accessability didn't factor that much into the thought process behind designing that website.
For me in general "thin dark fonts on bright BG" and "bright fonts on very dark BG" are both straining to the eyes although the former is worse almost every time. I find myself zooming in further and more often on websites with those sorts of color schemes although if I zoom too far in I then have to swivel my head back and forth for every line of text due to my glasses having "progressive lenses"[0] ie. a pretty narrow cone of vision with the right "power" to read at eye-screen distance.
> testing for these sorts of accessibility issues during development
- IMO a pretty good rule of thumb would be to not cover vast amounts of the website in bright colors
- offer a dark mode, maybe even make it the default with an optional light-mode
- respect the user's browser/system-colorscheme with the CSS property "color-scheme" [1] (although in Firefox the support for that feature is scheduled for the next version this coming January)
[0]: https://en.wikipedia.org/wiki/Progressive_lens
[1]: https://developer.mozilla.org/en-US/docs/Web/CSS/color-schem...
Yellow on black tends to make the writing “shrink” for me, lowering the readability.
Also the switching of the FG and BG colors was just an example I could think of in the moment to get something like "dark mode" with minimal effort. In practice I'd probably go with a somewhat "off-white"(?) FG on a medium-dark grey BG. IMO a less bright white text color in this scenario does well in eliminating the "shrinking" you speak of while the contrast with the muted grey BG isn't too harsh.
We seem to have slightly different access needs. This highlights the richness of working on accessibility problems. No one solution suits everyone, and there isn’t even a “accessible” and “not-accessible” pair that covers all bases either.