System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 980/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 452.06

Blender Version
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-07 08:12, hash: rBb351607996e4

Short description of error
The latest build has a broken UI. At some point I couldn't even save my project, but I couldn't reproduce it in a short timespan.

Exact steps for others to reproduce the error

I just opened the Blender 2.91 Alpha and got greeted by this.