TwentyTwelve: Lose Gap Above Header Image

Here is a practice site I’m using to teach myself the basics of CSS: https://sample2.mahonebaywebdesign.com/

I just want to get rid of the white space above the banner image. I’ve tried using the web developer toolbar in Firefox to isolate that element and have not had any luck. I can see it has something to do with .page or #masthead or some combination thereof, but nothing I do in my child theme’s CSS page seems to alter it and I cannot find it in the Edit CSS portion of the developer toolbar either. I’m sure whatever this is is very simple but I can’t figure it out. Any help appreciated. Thanks.