Extremely pretty stuff like dark clothing? (7)
I believe the answer is:
pyjamas
'dark clothing?' is the definition.
(clothing worn at night, when it's dark)
'extremely pretty stuff like' is the wordplay.
'extremely' means to remove the middle letters.
'stuff' becomes 'jam' (jamming is a kind of stuffing**).
'like' becomes 'as'.
'pretty' with its centre taken out is 'py'.
'py'+'jam'+'as'='PYJAMAS'
(Other definitions for pyjamas that I've seen before include "Sleeping suit" , "Sleeping-suit" , "Nightwear" , "Nightclothes" , "Jam a spy into these at night" .)