How did the Nicholas Brothers develop the style called classical tap?

The Nicholas Brothers, Fayard and Harold, developed the style known as classical tap by synthesizing diverse dance traditions into a singular, sophisticated performance art.1

Their approach combined the following elements:
* Jazz dance: Incorporating the rhythmic energy and movement vocabulary of jazz.1
* Ballet: Integrating the grace and upper-body fluidity characteristic of 20th-century ballet.12
* Acrobatics: Utilizing daring, athletic feats—such as leaps into full splits—to elevate the visual impact of their routines.12
* Tap dancing: Maintaining precise, percussive, and syncopated footwork as the foundation of their performance.12

By blending these disciplines with impeccable showmanship and elegance, the brothers elevated tap beyond the era's standard "hoofer" routines. They were known for performing in formal attire, which further distinguished their "class" style of precision dancing.12