Shrink logo (HUGE) on password-protected page

I have a password-protected page on my client’s website. When a first-time visitor is prompted to enter their password, the page where they enter it has a way-too-large picture of my band’s logo on top of it and so it’s cut off. We just want to shrink it down so it looks nicer but can’t find out how to do that.

Link and login in the private content section.

Thanks!

~J