Based on references uncovered in open-source WebKit code, it seems that Apple is working on a future Safari feature that would provide a Dark mode user choice for certain websites.
GitHub-hosted WebKit code refers to the new option as “overriding the system color-scheme with a per-website choice,” which 9to5Mac found in the WebKit source. A webpage in Dark mode would, for example, be accessible even when the system’s Light setting is on.
Users may now override the default setting for iOS 13’s dark mode by enabling an option in the settings menu of their apps. Users may now set a new per-website choice in Safari that allows them to choose whether or not a site displays correctly in either Light or Dark mode.
Additionally, Apple is working on a feature that would allow Safari users to ban modal popups on specified websites. Modal popups, which seem like system notifications and must be ignored by hitting the Cancel or another button, might appear on your screen. Apple is also working on a new API to handle the cookie consent process, which is used by many websites.
So far, the new WebKit capabilities have been labelled “TBA,” or “to be announced,” so it’s not obvious if they’ll be accessible to use in Safari through future iOS 15 and macOS 12 updates or later this year, when the new operating systems are introduced. Source