What did you do previously?
Did you make some changes on the PHP files? (if so, what PHP files you modified)
Or did you make some CSS changes? (if so what CSS rules you modified, if you remember)
Installing CleanMart might override your changes. (most likely your CSS changes) because CleanMart uses CSS override to stylize the Virtuemart related pages.
First I need to be sure what you have done. Then if sections' stylization will be eliminated from CleanMart, you will get your previous stylization(design) back.
Finally, you should also provide me your website URL where i can see the source codes and investigate deeply.
Regards
Support