when badges with and without highlighted state have a very
different brightness (as they might do in dark mode), hardcoding
the fg color of a badge independent of it's highlighted state
to $accent-fg-color doesn't work well, so add an extra SASS
variable we can reassign to something more specific in the custom theme
these values are not exactly the same as the palette values,
so we're essentially flattening the color palette used in the
theme, but this is needed when assigning custom colors for it
to look good.
Bruno Windels