The crux of the problem: I worked for some time in Intellij Idea and switched to Visual Studio 2017. The interfaces in Sharpe are written starting with "I", but how to visually distinguish a class from an interface as Ideas? How can I change the interface icon? 
- Here you also have a thought that it is strange that developers do not know how to combine quality and design? Either one or the other ... - Aqua
- 2The VS screen shows the files . In C #, one file can contain not one, but many classes, interfaces, and another. Therefore, the icon is always the same: the file icon. Click on the arrow, expand the contents - and see the icons of classes, interfaces, etc. - Alexander Petrov
2 answers
I think it will not be possible to change, but it is possible to distinguish. If you "open" the c # -file, then not only it is possible to distinguish classes and interfaces, but also methods, properties, events, ... 
See here: Class View and Object Browser icons
If you really need Intellij Idea icons, then look at the product from this company for the studio, called ReSharper.
If you go to the settings ( ReSharper - Options... ), then you can notice an item called Source code symbols theme , in which you can select the icons that interest you.
True, they are not entirely, and they are used only in IntelliSense hints, but for everyone there is a convenience, maybe this option will be more familiar to you.
- Then take Rider instead of VS - Andrew NOP
- @AndrewNOP Well, the question is about VS, I just share what I know. For me personally, the question of choosing icons is not at all clear, for it will not be difficult for me personally to get used to new icons. But we are all different ... - EvgeniyZ

