。
I can't agree with your idea.
Literal
I [topic-は] you [possessive-の] thinking [to-には] agree-cannot.
賛成できない ('can't agree') — 賛成する ('to agree') in potential negative form. には here combines に (target of agreement) with は (topical/contrastive emphasis). 考え (かんがえ, 'thinking, idea, opinion').