It's almost been a year since Microsoft officially announced Fluent Design, which had been formerly known as "Project NEON", introducing elements such as "acrylic" that implements a blurred translucency to the user interface. There have also been other subtle lighting effects added, such as highlighting, that follow your mouse cursor as it hovers over an object in a list, as an example. While Fluent Design has already been applied to a number of Microsoft's own apps, including Skype, Groove Music, and the Xbox app, as well as Windows 10, the design language now appears to be rolling out to the Microsoft Account portal.
The new design is somewhat of a departure from the existing one, although the account navigation elements are retained at the top of the portal. Below them is a new header containing the account holder's name and other high-level information such as Microsoft Rewards points and associated devices. The rest of the page is dedicated to a grid layout of the major account management sections and their corresponding categories which may help expose functions that would have otherwise required clicking through to each section to locate. Each object in the grid also pops out slightly when hovered over which may also trigger a short animation as an added touch.
At present, it seems that the interface update is in the early stages of becoming available so don't be too surprised if you log in and find that your account portal has not yet picked up the new layout but hopefully it won't be too long before it is fully deployed.