dotnet/aspnetcore ? reverse-engineered prompt

I want to build a modern web application using the ASP.NET Core framework. It needs to be cross-platform so that it can be developed and run on Windows, Mac, or Linux.

Let's start with a solid foundation for a cloud-based application. Create a project that has a simple front-end with a few pages—like a home page, an about page, and a contact page. It should also include a basic backend API. For now, the API can just have a simple endpoint that returns a "Hello, World!" style message.

I know this stack uses C# and .NET. Please structure the project following current best practices for building a responsive web app that could later connect to a database or be deployed to the cloud.