The word 'elaborate' refers to a detailed and complicated design or planning.
Option A, decorative refers to making something look more attractive and ornamental.
Option B, short refers to something relatively small in extent.
Option C, brief refers to a condensation or an abstract of an larger document or series of documents.
Option D, detailed refers to something having many details or facts.
Thus, according to the meaning, the word 'brief' is the antonym of the word 'elaborate'.