Xiaomi seems to have leaked a small portion of its MIUI 12 user interface by accident. It's widely believed that the Chinese OEM is busy working on the latest version of its Android overlay and there has even been a recent leak listing which smartphones will be supposedly first to receive MIUI 12. The latest user interface seems to have a darker appearance overall.
https://www.notebookcheck.net/Xiaomi-leaks-part-of-its-MIUI-12-user-interface-by-mistake.461663.0.html