。
Either one is fine with me.
Literal
I [topic-は] whichever fine is.
どっち is the casual contraction of どちら ('which one of two'), and どっちでも = 'whichever / either one.' 結構です here is a polite set phrase meaning 'that's fine / no problem' — note that 結構です can also mean 'no thank you' as a refusal, depending entirely on context and intonation.