This is a pwa blazor demo. Just go to the website "https://pwa-blazor-offline.azurewebsites.net", install the app as PWA APP (chrome: go to settings (top-right corner) and click install pwa app). Now you can disconect to the internet and still view the app. All files a cached on the device.
The app is made with blazor, so you can execute C# code on the client side.
If you want to start the app local, i think you will need visual studio 2019 (version 16.1.1) and dotnet core (version 3.0.100-preview-5-011568). The versions are the minimum requirements.