Container of something topping (6)
I believe the answer is:
hatbox
'container' is the definition.
(hatbox is a kind of container)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for hatbox that I've seen before include "Container for headwear" , "Milliner's container" , "Ten-gallon container maybe" , "Case for toppers" , "Case for storing headgear" .)