“Boogie-Doodle” (1948) IMDb
Norman McLaren (director).
To begin with, a black two-dimensional heart chases an embossed blue dot as it bounces between two lines on a red field, accompanied by a merry piano.
Abstract short with a multilingual opening including my native Swedish. Pen and ink directly onto film. The three-dimensional effect adds character very nicely.
References here: Porco Rosso (1992).