User2103319870 posted
use text editor to add a new .ccs file inside \Content of my project folder.Then I goto VS2017 Solution Explorer and click refresh. This .CSS file does not appear.
How to ask VS2017 to include it so I can use within VS?
Another option is to use Adding Existing option in Visual Studio IDE. Try the following steps
1) You can Right Click on Content folder -> Select
Add -> Existing Item -> Select the Folder path and addl the files to solution
You can Right Click on App_Themes folder -> Select Add -> Existing Item -> Select the Folder path and addl the files to solution