Style is the way that something is writing in, over the hidden meaning. Though they are very closely related and tend to be confused sometimes, there are not the one and the same. The style of a writing, whether it is professional or a personal piece, it includes diction and tone. They want to communicate the information to you in a certain way and consistency is vital in that. You can confuse readers if you switch from one style to another in a writing and ultimately, lose them.
Diction is your words you deiced to use in the piece. All words have a denotative and cognitive meaning, whether you want to believe me or not. If you say quirky, a trait, you are meaning to say the textbook definition of it but if you were to say it in a different way, as in odd, it can be received as a connotative words.
As for Tone, it is the word choice, attitude and ton of a piece as a whole. You cannot just look a one page of Harry Potter and assume that just because, *Spoiler alert* Dumbledoor dies in the fifth novel it is has an emotional tone. The tone of a novel can be emotional, logical, intimate, distant, serious, humorous, objective and subjective. There ultimately is not a write or wrong just as long as the tone stays consistent throughout out a piece.