Retaining margins of these, forgo random adjustment of shape and size (6)
I believe the answer is:
format
'size' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for format that I've seen before include "The shape and size, of a book say" , "Way of presentation" , "Prepare (a disk) for data" , "Arrangement or lay-out, say of book" , "The way something is arranged or set out" .)