What's the small bag behind the Japanese kimono?

In fact, it is a kimono belt, long, which is folded into a small bag at the back after several laps around the waist. It's just a decoration. There's nothing in it. Historically, this style was created by Japanese women drawing lessons from western clothing, which first appeared in the Edo period. The initial "small pocket" was put in front, and after several changes, it was finally decided to put it in the back. Nowadays, the "small pocket" behind the kimono has become one of the symbols of the kimono, which incorporates the beauty of the kimono.