"Square towel" is a kind of square soft hat promulgated in the early Ming Dynasty. A hat worn by officials and Confucian scholars;

"Blue shirt" means "gown". This stage is called "pleated ballet"

The special name of China opera costume (also known as pleated Taoist robe) is inclined collar gown.

Excerpt from Baidu Post Bar

This kind of clothes is the ordinary clothes of ordinary people. People with a little culture wear square towels. People who have never been to school tie their hair to their heads and tie it into a lock (nine means knotted hair).