La-di-da (4)
'la-di-da' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for arty that I've seen before include "Aesthetically pretentious" , "Bohemian" , "Dilettante" , "Pretentiously affected" , "Trendily into painting" .)
(Other definitions for posh that I've seen before include "Of the wealthy classes" , "Upper-class - Spice girl" , "Smart, stylish" , "Stylish (informal)" , "High-class" .)