How to properly implement a rubber SVG mask?

Question

css

Hello.
Can you please tell me how to properly implement a rubber SVG mask, a mask in general?
I'm trying to implement properties using css: At the moment everything has fallen down, I don't understand where the error is in SVG, the articles on the material are different, the implementation is the same. The code that is at the moment The goal is to implement a photo in a proportional triangle. Perhaps point out an error in the code or share a link to the material, demo. Thank you! mask: url(#masking);

Answer 1

code pen