Narrative style is tricky to pin down. Style is tone. Don’t forget that the narrative is essentially someone’s voice. The narrator is a character, not simply words dictating what happens in the story. Even if narration has an archaic, formal tone (such as often seen in classic literature or high fantasy), that is still the voice of a character, the one telling you a story of events as they perceived them to happen – even if omnipresent.
Style is how you structure sentences, how you use or abuse punctuation, how you describe scenery and character-thought-progression. It’s a combination of many writing techniques that you pick and perfect to work for not only your story, but for you as a writer.
I suppose one way to think of it is like poetry (we’re getting a bit hon hon darling now, but bear with me, it’s a metaphor). When you read a poem, you generally expect that poem to have rhythm – to have a way of twisting the structure of words on the page to either be staccato, flowing, or broken. You would expect a poem to scratch the surface of its real meaning – leaving you to infur the rest – or to expose the “character’s” emotional depth. The poem will paint every scene in vibrant colours, or it will be minimalistic and clean.
Writing a story is very much the same. Narrative style is one part you relating events as feels natural, two parts your character shouting into a microphone. Or whispering. I mean. It’s your style. Whatever.