Couponpress customization

I am looking for a customised CSS design for a wordpress package I have (couponpress - couponpress.com)
I have just looked into this and it says the wordpress I have, have Child Theme framework that lets you customize and build your own website design. I want to build a site similar to: www.Wowcher.co.uk

Please let me know if you can design CSS designs for existing themes or If you can design photoshop layers that can be converted into HTML/CSS onto site I will be happy to go with that also.

Please let me know how we could proceed with this?
Kind Regards