The error messages on login are styled as an alert (a colored box), but is currently wrapped in a span, which is display: inline by default. This causes visual problems when the text gets long enough (or the screen narrow enough) to cause line wrapping.

One option is to set display: block on the span but then you need to constrain it's width.

The other option is to remove the alert styling and just have red text.

For the short term I'd probably favour the latter.