There are various types of Citi online account web pages, depending on which kind of card you have. I have to have a different login for personal AA cards, business AA cards, Hilton HHonors cards, and my AT&T Universal card (which is a ThankYou points card). And the screens at each look completely different and hold different kinds of information.
So please explain which exact kind of Citi card you're logging in for. The person who responded that they have no problem may be logging in for a different card than the person who is having the problem, and the problem may be specific to the login for one kind of card (which the person having the problem has).
I also had no trouble logging in earlier today to my personal AA card account, but that's the only kind of Citi credit card account I've logged into for the past few days.