How to create a separate tpl with your own design in Simpla and link it to the base?

Question

CMS

I can not solve the problem in CMS Simpla in any way. I have a website that sells products. So, for some special products, for example, there is a promotion for this product, I wanted to create a promo page. You can, of course, bind a simple html-ku, but this option does not suit me. I would like to somehow add a new .tpl design to the site, since they have the same header, and I have a dynamic menu in the header. So, if I just connect the html file to my project, then the menu dynamics will not work on html. How can I solve this problem?