What is the tonality and harmony of Chopin's 'Raindrop' Prelude No.15 Op.28?

Tonality:
Tonic key: Db major in Section A. Modulation to C# minor, the enharmonic tonic minor, in Section B. Repeat of Section A, Db major.

Harmony:
Mainly diatonic, with some/occasional chromaticism
Use of a dominant pedal (repeated Abs)