We tried to use modern materials, but they didn't fit in with the building's classic style.

fit 在这里是动词，意思是"适合、相配"。 in 是介词，表示"在...方面"或"与...相关"。 with 是介词，表示"与...一起"或"与...相关"。 fit in with 是一个短语动词，意思是"与...协调、相配"，指某事物与其他事物在风格或特性上相匹配。