CSS-only implementation of an “osu!”-like circle-clicking rhythm game

For context, “osu!” is already a clone of a series which originated on Nintendo DS, Osu! Tatakae! Ouendan / Elite Beat Agents:

https://en.wikipedia.org/wiki/%C5%8Cendan

https://en.wikipedia.org/wiki/Osu!_Tatakae!_Ouendan_(series)

<https://en.wikipedia.org/wiki/Osu!>