It's a Chinese food buffet, but besides Chinese food they also have Italian food like pizza.

besides 是一个介词，意思是"除了...之外还有"，表示在原有事物基础上还有额外的内容。它由前缀 be-（表示"在...周围"）和 side（"边、面"）组成，字面意思是"在...的旁边"，引申为"除此之外"。