The name WebHost does not exists in current context

WebHost class resides Microsoft.AspNetCore assembly that comes with Microsoft.AspNetCore.All NuGet package. So to fix you problem install this NuGet package and add following using directive to your source file:

using Microsoft.AspNetCore;

As CodeFuller's answer indicated the WebHost class is available in the assembly Microsoft.AspNetCore If you don't need everything, you can just get the package Microsoft.AspNetCore.