How's about "Everything in it is superficial"? (7)
I believe the answer is:
shallow
'it is superficial?' is the definition.
('shallow' can be similar in meaning to 'superficial')
'how's about everything in' is the wordplay.
'about' is an anagram indicator.
'everything' becomes 'all' (all things).
'in' indicates putting letters inside.
'hows' is an anagram of 'show'.
'show' placed around 'all' is 'SHALLOW'.
(Other definitions for shallow that I've seen before include "Superficial" , "Lacking depth" , "justice" , "incapable of serious thought" , "Frivolous" .)