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