i want to build a fancy responsive Web and mobile app

Hi @Abduerhman Salama, 

Could you provide more detail into what your question entails and how it specifically pertains to K2-Cloud? This would help to answer your question or provide some tips.

If you are looking for ways to customize your SmartForms on K2 Cloud then the Style Profile is likely what you are looking for. You can find more information on the following help page for K2 Cloud: Style Profile

If you are looking for hands on assistance with your solution development then I would highly recommend reaching out to our Professional Services team. Professional Services is a separate team of K2 experts that specifically assist with requests of this nature. Please note that an engagement with the Professional Services team is a paid service thus it will incur additional costs. For more information please see here: https://www.nintex.com/customer-success/professional-services/