It expresses indifference about margin being raised? (3)
I believe the answer is:
meh
'it expresses indifference' is the definition.
('meh' is an expression of indifference)
'margin being raised?' is the wordplay.
'margin' becomes 'hem' (I've seen this in another clue).
'being raised?' is a reversal indicator (going up in a down clue).
'hem' in reverse letter order is 'MEH'.
'about' acts as a link.
(Other definitions for meh that I've seen before include "Who cares" , "am I bovvered?" , "Unexciting (modern slang)" , "Not much cop" , "expression of indifference" .)