The design of the amber room was in the fancy style popular in those days.中popular 的成分
问题描述：
The design of the amber room was in the fancy style popular in those days.中popular 的成分
答
这个句子的完整地说应该是这样的：
The design of the amber room was in the fancy style which was popular in those days.
“which was”被省略.
popular应该是作表语.