Windows search box is black

Question

My Windows 10 search box is black! It doesn't search anything.

I remember that shortly before this happened, I was annoyed with Cortana and toyed with the idea of disabling it. I didn't actually disable it and am not sure I changed anything. So I'm not sure if this is related or not.

I've tried using System Restore to back up to a time before the problem started. It didn't help. I've also found a lot of material online about blank search boxes. Judging by the images with that material, it seems to be a different problem. In any case, I've tried a lot of the suggestions for that problem. But they don't help either.

How can I fix this?