Dancers attend the Opera Ball at the State Opera House in Vienna, Austria, Feb. 20, 2020. The 2020 Vienna Opera Ball was held on Thursday night. (Photos: Xinhua)

Dancers attend the Opera Ball at the State Opera House in Vienna, Austria, Feb. 20, 2020. The 2020 Vienna Opera Ball was held on Thursday night.

Dancers attend the Opera Ball at the State Opera House in Vienna, Austria, Feb. 20, 2020. The 2020 Vienna Opera Ball was held on Thursday night.

Dancers attend the Opera Ball at the State Opera House in Vienna, Austria, Feb. 20, 2020. The 2020 Vienna Opera Ball was held on Thursday night.

Dancers attend the Opera Ball at the State Opera House in Vienna, Austria, Feb. 20, 2020. The 2020 Vienna Opera Ball was held on Thursday night.

Dancers attend the Opera Ball at the State Opera House in Vienna, Austria, Feb. 20, 2020. The 2020 Vienna Opera Ball was held on Thursday night.

Dancers attend the Opera Ball at the State Opera House in Vienna, Austria, Feb. 20, 2020. The 2020 Vienna Opera Ball was held on Thursday night.

Dancers attend the Opera Ball at the State Opera House in Vienna, Austria, Feb. 20, 2020. The 2020 Vienna Opera Ball was held on Thursday night.