Moonlight in Nice somewhat uplifting, don't you agree, mate? (5)
I believe the answer is:
innit
'don't you agree mate?' is the definition.
(informal way of saying 'isn't it?')
'moonlight in nice somewhat uplifting' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'uplifting' says the letters should be written in reverse.
'tinni' can be found hidden inside 'moonlight in nice'.
'tinni' written backwards gives 'INNIT'.
(Other definitions for innit that I've seen before include "tag question" , "Common question" , "word of emphasis" , "that produces stress for some" , "do you agree?" .)