[css-images-3] /TR page for of css-images-3 has unreadable tooltips, if you have a dark color-scheme preference

[dholbert]

STR:

1. Set a dark color-scheme preference in your browser (or your OS, if your browser defers to your OS).
   (You can confirm that this worked by e.g. visiting https://bugzilla.mozilla.org/ which will load with a nearly black background color if you've got a dark color-scheme preference.)
2. Visit https://www.w3.org/TR/css-images-3/
3. Hover any of the linked terms in the spec, e.g. the term <image> in the Abstract section at the very beginning. Look at the info tooltip that gets popped up for that term.

ACTUAL RESULTS:
The tooltip contents are unreadable - black text / dark-blue links, on dark-gray background.

EXPECTED RESULTS:
Readable tooltip.

Here's a screenshot:

This reproduces in all browsers (I tested Firefox, Chrome, and Safari.) Essentially it looks like this page's styles don't take the user's color-scheme preference into account, which is ~fine, except that the page does take the color-scheme into account specifically for determining the background-color of the tooltip.

[dholbert]

(I have a nagging feeling that I might've filed a version of this previously, but I'm not sure and wasn't able to immediately find it in my browser history.)