Increase Width Sign Up Form & Set Default Dial Code

Hello,

I would like to increase the width of the “Sign up form” block in order to have better visibility of the telephone number field (see countries). Do you know how to do this? Secondly, is it possible to set a default value? In my case, I know that most of the users are Australian, so I’d like to set the default Australian dial in the phone field.

Thanks for your help,