From the Wikimedia Blog:
This week we pushed several new and updated design changes to our beta. We hope these changes will provide a more professional look and a better experience for you. These include changes to the footer, a cleaner design for revealing and hiding sections, and a revamped full-screen search experience. The mechanism for toggling between desktop and mobile has also moved from the footer to the top navigation menu to the left of search to allow users to switch more effortlessly.
In addition to this we have also pushed an experimental feature which makes it easier to refer to references on articles without having to plunge to the bottom of the page. Now clicking on a reference will load an overlay which readers can consult without losing their place in the article.
Learn More About the Face Lift in the Complete Blog Post