Me as a mobile app developer trying to add a button to a page of a .Net website:
So, what do i need to do?

Web developer:
Oh that's easy. You need to edit that template which produces html, add an event in there that will call a javascript function, which is in a .js file, which is generated from a typescript file. Than you should give that button a style. Simply by opening up that .less file here and adding a class which will be translated to css later. In that c# file over there you add a bundle reference which contains the css and js files, but before that, they must be minified. In that other c# file, you add a controller that handles your button.
Aaand... take care of new js features and css features. Most browsers don't support them. Those cool C#7 features you love so much... not in this project. Our build servers don't support C#7. Those new features are evil anyway.

😭