Performers sing to patients and medical workers in the open air at Clinical Hospital Dubrava, the designated hospital for treating COVID-19 patients, in Zagreb, Croatia, Dec. 25, 2020. (Tomislav Miletic/Pixsell via Xinhua)

A medical worker watches open-air performance for hospitalized children and medical workers at Children's Hospital Zagreb in Zagreb, Croatia, Dec. 25, 2020. (Goran Stanzl/Pixsell via Xinhua)

Performers sing to patients and medical workers in the open air at Clinical Hospital Dubrava, the designated hospital for treating COVID-19 patients, in Zagreb, Croatia, Dec. 25, 2020. (Tomislav Miletic/Pixsell via Xinhua)