The MediaWiki developers have been slowly improving the accessibility of the user interface. The next step in this transition will change the appearance of some buttons and may break some outdated (non-updated or unmaintained) user scripts and gadgets.
You can see and use the old and new versions now. Most editors will only notice that some buttons are slightly larger and have different colors.
Comparison of old and new styles
Buttons before the change
Buttons after the change
However, this change also affects some user scripts and gadgets. Unfortunately, some of them may not work well in the new system. If you maintain any user scripts or gadgets that are used for editing, please see mw:Contributors/Projects/Accessible editing buttons for information on how to test and fix your scripts. Outdated scripts can be tested and fixed now.
A quick update on the progress of enabling Page Previews (previously named Hovercards) on this project. Page Previews provide a preview of any linked article, giving readers a quick understanding of a related article without leaving the current page. As mentioned in December we're preparing to remove the feature from Beta and make it the default behavior for logged-out users. We have recently made a large update to the code which fixes most outstanding bugs.
Due to some issues with our instrumentation, we delayed our deployment by a few months. We are finally ready to deploy the feature. Page Previews will be off by default and available in the user preferences page for logged-in users the week of July 24th. The feature will be on by default for current beta users and logged-out users. If you would like to preview the feature, you can enable it as a beta feature. For more information see Page Previews. Questions can be left on the talk page in your preferred language.