Sure about nice art (7)
I believe the answer is:
certain
'sure' is the definition.
(I know that sure can be written as certain)
'about nice art' is the wordplay.
'about' indicates anagramming the letters.
'nice'+'art'='niceart'
'niceart' with letters rearranged gives 'CERTAIN'.
(Other definitions for certain that I've seen before include "Proved beyond doubt" , "Known beyond doubt" , "Unquestionable" , "Decided" , "Indisputable" .)