@jbrandon. An option titled 'Enable dark theme' has been made available –path: opera://settings/ , under category Basic, subcategory Appearance–. Yet targets to which that function applies are without doubt on purpose made restrictive as that observation cannot possibly be an issue. Those built-in pages Bookmarks, Personal News, History, Extensions, have been left in the UI team process out of consideration, and their readability illustrate still what an unfriendly eye-destructive over-lighted theme can be. Title 'Enable dark theme', comes along with no particular mention; therefore its application is meant to be global, while it currently applies only to the built-in page Settings.