This PR uses a pretty cool GPUI method called `blend` to make this
callout's background color not translucent.

| Before | Header |
|--------|--------|
| <img width="732" alt="Screenshot 2025-02-07 at 4 58 16 PM"
src="https://github.com/user-attachments/assets/2a5df61b-dfa0-4edc-bffa-a605a2aa491a"
/> | <img width="732" alt="Screenshot 2025-02-07 at 4 56 48 PM"
src="https://github.com/user-attachments/assets/5dee9fca-6239-4ae0-80f5-dcc6abf0e779"
/> |

Release Notes:

- N/A