[Theme: Twenty Twelve] Header with one color full width of body

Hey,

I enjoy working with twenty twelve theme because it’s simple and flexible.

However – I want to modify it.

1 – I want the header (banner) to go the full width of the “div id: PAGE”
(NOT the full width of the browser window)
2 – I then want to style that with a background color.

Basically make it old school. But the banner is governed by the padding in the “body .site” style.

body .site {
    box-shadow: 0 2px 6px rgba(100, 100, 100, 0.3);
    margin-bottom: 3.42857rem;
    margin-top: 3.42857rem;
    <strong>padding: 0 2.85714rem;</strong>
}

Can someone give me some tips on how to approach this.

Thanks!