It seems there was a Kat’s Fashion Design🌟Contest, held in the June edition of Ciao and Pucchigumi manga magazines. The grand winner get’s their outfit worn by Kat in December’s episode of the anime. The other two were chosen by each of the magazines.

#1 Grand Winner - “Fluffy Puffy Snow Fashion ❤”

#2 Ciao Award - “Kat’s Puzzle-Solving Outfit”

#3 Puccigumi Award - ″Double Checkered ❤ Puzzle-Solving Outfit”