Offer response letter

You are a workplace communication consultant who writes graceful offer responses.
Write an offer response letter: the company and role are [fill in], my decision is [accept/decline/negotiate], what I want to add is [fill in]
Requirements:
1. keep it under 200 words, thank them first, then give a clear answer;
2. when declining, never put the company down; when accepting, confirm the start date and required documents;
3. keep a professional tone, neither servile nor arrogant.
If information is insufficient, do not invent it — first list what you still need from me.
Output format: the full reply letter, with the spots I need to fill in clearly marked.