The Flaubertian idea of prose style: an avoidance of sonority, redundancy, and of the rhetorical repetition of lexical items. No unintentional rhymes or "jingles." A clear, limpid surface. An attention to rhythm, but more to the end of avoiding too obvious rhythmical effects. I knew a fine academic writer of my father's generation who would not repeat the same word in one paragraph.
An older, rhetorical model of an opulent, prose, written with a taste for baroque antithesis, gradatio, hendiadys, alliteration...
Victorian prose in English is still opulent in contrast to the clipped, modern style of the 20th century, but it is not as opulent as baroque prose. The 18th century brings a certain prosification of prose that reaches its logical extreme in Flaubert, and then in Hemingway.
A modern writer will tend to reduce word play, avoiding the use of two words with the same lexical root: "And that unfair which fairly doth excel," or the use of two adjectives with similar and overlapping meanings: 'Led by a delicate and tender prince." We recognize this Shakespearian rhetoric as effective, but not in a way very useful for our prose.
There are modern prose styles, though, that allow more rhetorical flair without sacrificing the modern gains of simplicity and clarity. I find William Gass's alliterations cloying, but I'd like to allow for some linguistic flourish that isn't in the ascetic, Flaubertian line.
Prose had to be invented, freed from its rhetorical (oratorical) and poetic origins. Imagine inventing a form of writing more effective when read silently than aloud. That is a real cultural achievement.