Username bar too long...where to change?

Hi: the username bar in the login page is too long. Here's the image.
Which file should I edit and what line?

Thanks in advance
Arezki

forms editor , sign up , you must of changed something there?

or

setup

Signup Form Configuration

i have mine set to 6-32 for username

Arezki it is always helpful if you give a link to this page so people can view it in a browser and use software to see what css instructions the display is acting on. Suggestions can then be made.

With an image the only conclusion is 'That's not right'.