Complex sentence: Post-grunge is a genre of music that emerged in the 1990s as a derivative of grunge, using the sounds and aesthetic of grunge, but with a more commercially accessible tone.
Split into simpler sentences: Post-grunge is a genre of music that emerged in the 1990s. Post-grunge later became a derivative of grunge, using the sounds and aesthetics of grunge, but with a more commercially accessible tone.