The `inverted-selection` rules defined in the `%brand-background`
selector weren't being applied because we were using this selector in
`::before` and `::after` pseudoelements. Not sure about the reason, but
it looks like the saturation of `::after::selection` pseudoelements
resulted in invalid selectors and so the inverted selection rules were
ignored for every selection using `%brand-background`, like
`%budget-header`.
Using `@include brand-background` instead of `@extend %brand-background`
in pseudoelements solves the issue. The inverted selection might not
work in these pseudoelements, but we don't need it there since these
pseudoelements don't have content.