One seeking perfection? One limited by silly details (8)
I believe the answer is:
idealist
'one seeking perfection?' is the definition.
(someone who wants a perfect world)
'one limited by silly details' is the wordplay.
'one' becomes 'I' (Roman numeral).
'limited by' means one lot of letters goes inside another (limit can mean to contain or border off).
'silly' indicates anagramming the letters.
'details' is an anagram of 'idealst'.
'i' going within 'idealst' is 'IDEALIST'.
(Other definitions for idealist that I've seen before include "One who aims for perfection, may be unrealistic" , "Visionary" , "Utopian" , "Person striving for perfection" , "One who aspires to perfect standards" .)