This plugin provides filetype support — including syntax highlighting and indentation — for Razor markup files. Out of the box, it detects *.cshtml and *.razor files.
Custom highlighting is defined for HTML and C# by this plugin in order to ensure that they are properly integrated; this highlighting will only affect Razor files, not regular HTML and C# files. If you'd like to use the C# highlighting for regular C# files as well, you can install my vim-cs plugin.
This is a standard Vim plugin which can be installed using your plugin manager of choice. If you do not already have a plugin manager, I recommend vim-plug.