AEM default login component cant validate user..

I have dragged and dropped the default login component from general group present in sidekick into the parsys. for more clear idea, pl see the attached image file. when i try to login its saying the user could not be found always, whatever credentials i give. I am new to AEM and couldn't get what is happening? from where it is validating the credentials. ?? if we want to add a specific user, what can be done so that the given user could be identified while login. Also, where is the css file present for that login component? If we want to add our personal CSS what can be done?? Thanks in advance.!! :)