It is one of the windows that do not have keyboard focus.

Repro:
1. Open Unity Editor with a new or existing project
2. Go to Game view window
3. Click on the "Aspect Ratio" drop-down menu between Display and Scale in the menu bar on top of the Game view window.
4. Click on the "Add" at the bottom of the drop-down menu.
5. A new window pops out called "Add".
6. Try to try in Label or Width & Height.

Expected: The "Add" window takes keyboard input.
Actual: The "Add" window does not take keyboard input.