replace 'opacity' in CSS

In the CSS we use opacity to gray out stories and comments with negative scores. This has prompted recurring bugs over the years because opacity creates a stacking context, sometimes child elements like the popups for caches and flags appear under other elements. And then those inherit the opacity so they're hard to see. (These two bugs have recurred roughly annually for the life of the site.)

We have a light and a dark mode, and high contrast modes. This is not a huge matrix of potential colors for this effect. Can we precalculate those values and use the colors directly on the text color attribute? Then we wouldn't have a growing list of :not exclusions on the opacity like #2024.