Responisve HTML not working

Responisve HTML not working

Hello, we made a responsive html email , however, w hen copying the html into the template builder, the responsiveness of the email stops working. 
I have been reading on the forum about others having this same problem before. So I`ll make the same question:  Is it only the premade templates that can be made responsive in zoho campaigns or is there some trick to making the custom template responsive? 

Thank you!