dark-mode-pass.txt
Add a dark theme to this: <paste the CSS>

- Pull every colour into CSS custom properties first, then override
  only those properties for dark. Don't duplicate the stylesheet.
- Follow prefers-color-scheme by default.
- Pure black and pure white are both wrong. Say what you used instead.
- Check contrast in both themes, and tell me anything that fails.

Watch for colours hidden in shadows, borders and SVG fills.

Shadows are the giveaway. A drop shadow tuned for a white page turns into a smudge on a dark one.