Literary style refers to the overall way in which words are used by a writer to communicate with an audience; "the characteristic mode of construction and expression in writing and speaking." A writer's style may involve use of certain patterns of sentence construction, a characteristic vocabulary, or particular focus upon specific aspects of description of setting or characters or action.
Rhetorical devices are specific ways of using words to create a specific effect. Alliteration, when many words begin with the same initial sound, is a rhetorical device. Use of metaphor or simile is a rhetorical device. Figures of speech are rhetorical devices. All these are used to create or support the particular effect the author is building; they are part of the literary style that shapes the author's work.
Mark Twain, for example, uses a literary style that includes extensive use of dialect to add individuality to his characters. Huck's description of the supper at the Wilks's home follows that style, using rhetorical devices including figures of speech, alliteration, and rhyming words to add to the personality of the narrator.
Mary Jane she set at the head of the table, with Susan along side of her, and said how bad the biscuits was, and how mean the preserves was, and how ornery and tough the fried chickens was-and all that kind of rot, the way women always do for to force out compliments; and the people all knowed everything was tip-top, and said so-said 'How do you get biscuits to brown so nice?' and 'Where, for the land's sake did you get these amaz'n pickles?' and all that kind of hum-bug talky-talk, just the way people always does at a supper, you know.