issue about custom error page in web app service

I want to upload a customized html error pages instead of default html page. According to [ref](https://github.com/Azure/app-service-linux-docs/blob/master/HowTo/configure_custom_error_page.md), I could upload the html file to complete it. But in fact, I need to upload a html file and the html need other static files, such as images, css, js. I don't know how to upload it. Could you help me with this issue? Expect your reply.