@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.
But you should be log in as applicant: https://praca.by/applicant/register/
HTTP_USER_AGENT: Mozilla/5.0 (iPhone; CPU iPhone OS 11_2_6 like Mac OS AppleWebKit/604.5.6 (KHTML, like Gecko) OPiOS/184.108.40.206049 Mobile/15D100 Safari/9537.53
the same as
Opera Mini 16 on iOS 11.2