Actually Jkreativ will support child themes and you can override the default style by using child theme. But in this case it will depend on your code, so please check again your code it works or not. I’m also install jkreativ on my localhost and it’s using child theme. Everything just work fine on my side.
If you can tell me the url of the page and what things that you want to change, it would be better i think so i can easily to help you out or give you an example.