Hello, 

That sounds like a strange request. I don't quite see why a Website will not be compatible with Pega. I guess he was talking about adding a Pega mashup inside said Website. 

Hi jezag279,

I think what you have been asked to do is to follow the pega suggested principles in designing and implementing the UI of your pega application.

You should visit the site https://design.pega.com/ where all design principles , components, and the standards are clearly given by PEGA.

Also when designing you UI and if there are plans to embed the pega as a gadget to external web application , called Pega Web Mashup, then the external application must be built in HTML5 standards to compatible with PEGA gadget.

Please go through the following link for information

https://community.pega.com/knowledgebase/capabilities/mobility/mashup-sdk/web-mashup

Please feel free to reply if you have any questions.

Thank you,

Regards, Cherb.

Why don't you ask this developer?