After an interview, formal tone
Sent the same afternoon. The second paragraph picks up one thing the interviewer said and ties it to a real result.
Subject: Thank you – Product Designer interview
Dear Ms. Shah, Thank you for taking the time to meet with me today about the Product Designer position at Northwind. I enjoyed our conversation and learning more about the team's work. I was particularly interested in our discussion of your plans to rebuild the onboarding flow. It connects closely to my own experience: I led a similar redesign at Brightwave that lifted sign-ups by 18%. Our conversation confirmed my interest in the role. If there is anything else I can provide, please let me know. Thank you again for your time. Kind regards, Alex Morgan