Having recently spent some time staring at the PasswordPrompt, while fixing issue 6010, I felt that the current border style does not really give a good visual indication that the input field actually has focus.
The current appearance was first introduced in PR 3527; but I don't know if having a different border style in Overlay dialogs was intentional, or if it just "happened".
However, given the colour palette used in the viewer UI, I think that using the same border style for all .toolbarFields makes sense.