The CSS specification is ever-evolving. The process for implementing new features in CSS is complicated, but the simplified version is that the CSS Working Group decides on the new elements to be added to the specification. It is then up to the browsers to implement these new elements, and the browsers choose in which order to implement them, which is why we now have a mismatch of support for new features. While this may be annoying at times, it's a much better way to do it than the browsers implementing the full specification, as we saw in the early days of the web.
The CSS Working Group is made up of members from all major browser vendors and other technology companies like Apple and Adobe. Apple, having recently launched its new version of MacOS, wanted a way to detect its snazzy new dark mode in the browser. In order to do this, Apple pushed a recommendation to the specification for a new level 5 media query.
Using this media query, we can detect if the user is currently using light or dark mode in the OS. At the moment this is only supported by Safari Technology Preview 69 and above, but the