This article will demonstrate creating a styled Offline page and updating the service worker's cache using an editable copy of the default service worker provided by the WebEssentials.AspNetCore.PWA NuGet package. I will assume you have created a new ASP.NET Core 2.2 Razor Pages project, have successfully installed the WebEssentials.AspNetCore.PWA package and have created an editable copy of the service worker. I won't use Identity or Individual User Accounts.
The WebEssentials.AspNetCore.PWA NuGet package dynamically creates an offline.html file which is displayed when the application is offline, and the resource has not been cached. It has little styling.