I’m doing manual QA for a responsive static website and want to define a professional set of screen sizes/devices for testing (mobile, tablet, desktop), including edge cases and in-between widths.

How do teams typically decide:

• Which viewport widths to test (e.g. 375, 768, 1440)?

• Whether to prioritize CSS breakpoints vs real device resolutions?

• How many real devices vs browser emulators to use?

• How to cover “in-between” widths where layout bugs often appear?

I’m looking for industry best practices or QA workflows.