In some cases, you may notice the "Compatibility Mode on" banner.

This mode is enabled when Web Publisher is viewed on Safari. Safari currently doesn't support WebContainers, which is the technology at the basis of Web Publisher.

That being said, you can still run Web Publisher and submit Pull Requests. In this mode, Web Publisher only renders a Markdown-to-HTML conversion. Your app itself it not being run, so there is no app-specific styling, and if you’re using some kind of components in your Markdown, they won’t be compiled.