Sweet face reflected decline (7)
I believe the answer is:
gumdrop
'sweet' is the definition.
(gumdrop is a kind of sweet)
'face reflected decline' is the wordplay.
'face' becomes 'mug' (informal term for face).
'reflected' shows that the letters should be reversed in order.
'decline' becomes 'drop' (dropping is a kind of declining).
'mug' reversed gives 'gum'.
'gum'+'drop'='GUMDROP'
(Other definitions for gumdrop that I've seen before include "It may be sucked" , "Firm jelly sweet" , "Gelatinous type of sweet" , "chew" , "Jelly-like sweet" .)