I would like to show an AppKit popover beside a HTML input field, exactly in the same way as the "New password" generator from operating system does it.
Is this possible? For the moment, the possibilities of using AppKit elements in Safari Extensions are very limited.
Specially now we need to support Dark Mode etc... it makes no more sense to simulate "AppKit" elements made by self in HTML5.
Your extension's popover is a native AppKit popover, but that can't be positioned next to an HTML input field like you are requesting.
However, if you created your own popover inside the web page, WebKit has support for dark mode, which you can check out at: