How much room is there after an offer? - 10 months and counting

I want to negotiate but I am afraid they will withdraw. I have read a lot of threads here and could not find my exact situation. The hiring manager was friendly and open. What wording worked?

Most employers expect a short conversation. Mine did not even blink.

I thanked them and said I was excited but hoped we could talk about the pay. They came back with a bit more.