Scale the background image.

Use the CSS3 background-size to size the background photo to its
containing element.
Apply the transparency to the page-header directly

The page-header will always need to be transparent, and it may not stay
in the shared layout for much longer, so apply the transparency effect
to the page-header class itself rather than via another class.
Up the opacity of the content blocks.

Black text on the 50% opaque background wasn't showing up too well.
It's more readable on a 75% opaque background.
Make page-header's underline red.

Use the red from the error class (#e80c4d), as it's a bit softer than
the basic #ff0000.
Fix the padding in the content boxes.

Use 12px all round for both the page-header and the body content
classes. Also strip out all margin from h1s inside page-header to ensure
the padding isn't too mahoosive.