serious music vs musical style

serious music and musical style both are nouns.

Word	Noun	Adjective	Verb	Adverb
serious music	Yes	No	No	No
musical style	Yes	No	No	No

As nouns, musical style is a hypernym of serious music; that is, musical style is a word with a broader meaning than serious music:

serious music: traditional genre of music conforming to an established form and appealing to critical interest and developed musical taste
musical style: an expressive style of music

Other hypernyms of serious music include music genre, musical genre.

serious music (noun)	musical style (noun)
traditional genre of music conforming to an established form and appealing to critical interest and developed musical taste	an expressive style of music