Web Add-ins

Using Visual Studio Editor

App.css and App.js got removed in Visual Studio 2017

visualstudio.com/features/office-tools-vs

link - msdn.microsoft.com/en-us/library/office/fp142161.aspx 

Latest Templates

link - github.com/OfficeDev/PnP-OfficeAddins/tree/master/Samples/Office.ASP.NETCoreReactAddins 

Office / SharePoint Templates

Benefits of using Visual Studio
create sample documents and injects the add-in into the document
provides a registry based document store and local web server to host the add-in
sets up a debugging environment