Apple appears to be working on an upcoming Safari feature that will introduce a Dark mode user preference for individual websites, based on references found in open-source WebKit code.
WebKit is Apple's browser engine that powers all browsers on iOS, and the new option, spotted by 9to5Mac, is referred in the GitHub-hosted WebKit code as "overriding the system color-scheme with a per-website preference." This should, for example, let users always view a particular website in Dark mode, even if the system's Light mode is enabled.
Since Apple introduced Dark mode for iPhone and iPad with iOS 13, developers have updated their app interfaces to match the system setting or allow users to override it. The new per-website preference in Safari would extend this option to browsing sites, and also let users correct for sites that don't display properly in either Light or Dark modes.
In addition to the per-website display setting, Apple is developing another option to block modal popups on specific websites viewed in Safari. Modal popups must be dismissed by tapping a Cancel or other button, and can look like system alerts. Apple also has a new API in the works to manage the process of cookie consent that many websites use.
The new WebKit features are labelled as "TBA," or to be announced, so it's unclear whether they will become available to use in Safari via future iOS 15 and macOS 12 updates or later in the year when the new operating system versions are released.
