According to the query of Netease Cloud Music, the smiling face of young people is the lyrics of the song "Yellow Photo" sung by singer Zhang Kaili, written by Zhang Jianquan and composer Meng Wenhao.
Part of the lyrics: a yellow photo frames our youthful appearance, and a young smiling face records our thousands of stories. White hair has crept into my ear, and time is gone forever. Whenever the sun sets, my heart is full of sadness.