Is there any workaround to add material design with frappe portal?
Not in a simple way. You could create a custom app and then override all of the template files. It’d be a big project, but probably doable.
Is it possible to add an angular app with portal?
Possibly. I don’t know much about angular, but I suspect you could get the library loaded and running on html components. At some point, though, I imagine you’d start conflicting with Frappe’s framework for things like routing, etc.
Thanks for your suggestion, I have one more question. While extending a base page at frappe portal I lost the connection with js file corresponding to an html file. Why?
Sorry, I couldn’t guess. You might find a clue in the server or debug logs.