It was written by bassist Mark Hoppus, and drummer Travis Barker, as well as producer Tim Pagnotta, and songwriter Sam Hollander.

Blink-182 bassist Mark Hoppus, who delivers solo vocals on the track,[1] developed the song's concept based on his own struggle with anxiety and depression, which had worsened when the band were recording Nine.

In the clip, which was entirely filmed on smartphones and vertically angled, pictures Hoppus, Barker, and Skiba performing from their homes, intercut with footage of fans and friends.

[7] The clip features cameos from various celebrities, including Steve-O, Machine Gun Kelly, the Used frontman Bert McCracken and Bella Thorne.

[10] Tom Breihan at Stereogum enjoyed the song, praising it as "heartfelt and catchy, and it's got that great Travis Barker drum-thunder underneath those pinched, hopeless hooks.

"[11] Mackenzie Cummings-Grady, writing for music blog Popdust, criticized the song as formulaic and overly nostalgic: "'Happy Days' shows that our favorite middle-aged musicians are lost in translation, unable to articulate exactly what kind of band they are anymore.