Casual mini with elegant top is reduced (8)
I believe the answer is:
careless
'casual' is the definition.
(similar in meaning)
'mini with elegant top is reduced' is the wordplay.
'mini with elegant top' becomes 'care' (I can't explain this - if you can you should give a lot more credence to this answer).
'is reduced' becomes 'less' (a reduced amount).
'care'+'less'='CARELESS'
Can you help me to learn more?
(Other definitions for careless that I've seen before include "Inattentive to risk" , "Inconsiderate" , "Negligent, unconcerned" , "Slapdash" , "'Heedless, unthinking (8)'" .)