How do I create an error page for my nativefier app for when there is no internet connection?

I'm a web developer. I recently found out about nativefier and have just used it. But the issue I'm having is that, if there's no internet connection, the nativefier desktop app just stays blank. I'd like to have an error page for when there's no internet connection that tells the user that he may need to connect the internet. Thanks

via Okoroafor Chukwuemeka