Both the `.active` colour and the `:focus` fix should be moved wherever `#proposition-links` is defined, which appears to be [govuk_template](https://github.com/alphagov/govuk_template/blob/master/source/assets/stylesheets/_header.scss).

Links being readable when active or focused isn't a Whitehall specific requirement of the header. Given the current pain involved in deploying changes involving static, whitehall and template I left this comment rather than do it. I've made a note to write it up as a story, and/or pass it over to the Elements team.