Fuchsia is based on a new kernel called Zircon.. The project became known in 2016 on Github without any official announcement.
Fuchsia's user interface and apps are written with Flutter, a software development kit allowing cross-platform development abilities for Fuchsia, Android and iOS. Flutter produces apps based on Dart, offering apps with high performance that run at 120 frames per second.
Flutter also offers a Vulkan-based graphics rendering engine called "Escher", with specific support for "Volumetric soft shadows", an element that Ars Technica wrote "seems custom-built to run Google's shadow-heavy 'Material Design' interface guidelines".
Although it's more on the technical side, the documentation concerning Fuchsia is located at the Google Source website & Document Page.