It would only give you the last character of the password though. You can use CSS selectors to check the start [value^=a] and anything in the middle [value*=a] as well though which can be revealing I imagine.
Well there's the start [value^=a], the end [value$=a] and the "anywhere" [value*=a] selectors.
In something like 13000 selectors you could easily get the first 2, last 2, and any characters in the middle that are in the password making targeted attacks significantly easier. (This is based on very-very rough napkin math assuming an ~80 character dictionary for upper/lower, numbers, and "symbols" since I didn't want to count)
That's a lot, but it's well within the realm of possibility (it looks like that would end up as about a 1mb css file)