So I designed this layout for my Tumblr page where the section of the blog with the posts is over a notebook paper. Above this is a header. On my computer, with the browser fully maximized, it looks great. But once it's minimized or the window is resized, the header and post section leaves the section with the paper.

Here is the blog for example: brendansdetour.tumblr.com

ALSO: On my sister's computer, the header is off-center and doesn't match the sheet of paper in the background.

Basically, is there a way to make this layout adjust fully to all resolutions and resizings? I've seen other tumblr layouts with extremely similar set-ups be able to do this.

Please help me out?

Thank you!