Design style, informally (4)

I believe the answer is:

'design style informally' is the definition.
(I've seen this in another clue)

This is the entire clue.

(Other definitions for deco that I've seen before include "Art's partner" , "Art -, C 20 style of ornamentation" , "Style of design popular in the 1920s and 1930s" .)

I've seen this clue in the Thinks.com.

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