Update nav button styles

Overview

Updated the retro page nav to use the teal/sea-foam colors instead of purple
Componentized the nav links and nav buttons because I was having style scoping issues.
Renamed color variables: $dark-turquoise is now $teal and $turquoise is now $sea-foam
Fixed the logout button icon in mobile (was previously the same as the download csv icon)

1) Go to the Retro Page in both light and dark mode. Ensure there is no longer purple in the nav and styles are updated.