Except for header background, you won’t need any other images. You can use a div for header with image background and 100% width, another div as the outer “square” with background and border and padding/margin, then div with white background and border radius (http://www.w3schools.com/cssref/css3_pr_border-radius.asp). (You could also do gradient from header background by using css3 but it’s not well adopted by browsers yet).
solved Build frame for page content using CSS [closed]