While you are editing a variable name in Visual Studio 2015, a dashed outline is displayed around it:
It’s a new feature of Visual Studio 2015 that works for C# and Visual Basic languages. The same outline is displayed when you change a method, class or namespace name.
If you find this outline distracting, install the free Plain Rename extension that completely removes it.
Making Visual Studio perfect 
Great, but it doesn’t work for cshtml pages 😦
v1.1 adds support for .cshtml files:
https://visualstudioextensions.vlasovstudio.com/2017/01/31/plain-rename-v1-1-adds-support-for-vs-2017-and-html-code/