Using light-dark for colors

[Gravy59]

Since light-dark is now baseline, it might be a good idea to use that syntax in v4 e.g.

@theme {
  --color-background: light-dark(theme(colors.white), theme(colors.zinc.950));
  --color-foreground: light-dark(theme(colors.zinc.950), theme(colors.zinc.50));
}

This would be more concise and also allow intellisense to inform which colors on hover: /* light-dark(theme(colors.zinc.950), theme(colors.zinc.50)) */