I'm still seeing a border on the screen when you have external login's configured @NguyenThuyLan:

It's a bit weird, as it's not always there. If I inspect the element it disapears but if I click back on the screen it comes back. So I don't think it's caching. I don't see this once I click to "Sign in with Umbraco".

The border is coming from the native <dialog /> element in the browser, I believe (MDN seems to confirm this). The screen with external login is technically a modal/dialog. You would probably need to interact directly with that element, and that may be hidden inside the <uui-popover-container /> element.

@iOvergaard I'm not sure how to fix this? Can you give me an example?
I can see it is affected by :focus-visible

@NguyenThuyLan uui-popover-container is something in the UI library, so the styling would need to go there. However, we cannot change all modals in the system to make this work. It is something of a "hack" to use the modal system to open the login form on top of the backoffice.
Perhaps it would be better suited to implement a native popover element just for the login form (with its own styling) rather than relying on UUI components.

This is the inner modal element: src/Umbraco.Web.UI.Client/src/packages/core/auth/modals/umb-app-auth-modal.element.ts

It is opened in UmbAppAuthController on line 130:

What if, instead of using the modal manager, we opened the element as a native popover, where we would be in control of the styling?