It also looks like the App Store will include video previews on the new macOS. In macOS 10.14 the dark user interface is also reflected in the apps like Xcode 10 and also icons get a darker treatment.
Also, when the video is carefully studied, its worth noting that, the trash icon also appears to be of a dark colour. The OS' current dark theme option only applies to the menu and dock bars.
First off, it's worth pointing out that the leak comes from a 30-second video preview of Xcode on macOS 10.14 that pops up in the Mac App Store API, so it's safe to assume the details are legit.
Apple has shown clear signs in recent times that it wants to try and unify the iOS and macOS experience, which means that the Mac App Store is likely to feature a similar redesign as iOS contained when iOS 11 was introduced a year ago. It looks a lot like the editing mode in the Photos app. This leak lines up with our previous reporting of dark mode appearance API references turning up in WebKit source code. Nonetheless, the new leaked build shows off a dark mode for a newer version of Xcode (10). The video hints at an upcoming dark mode as a system wide feature.
Behind all the window chrome, you can see a new Mac wallpaper. Apple will present iOS 12, tvOS 12 and watchOS 5 on Monday at 10 am PDT. There is a suggestion that one of the possible names for the macOS 10.14 is Mojave.
The desktop environment possibly is a picture of the Mojave Desert in California through the night, suggesting at a macOS Mojave sign for the succeeding version. We'll be bringing live coverage from the keynote itself so stay tuned - the show kicks off at 10 AM.