Open a new file, having 749x235 px and 72 dpi. Take the indicated tool

and create the lowest background of the site’s header to be.
Blending Options-Gradient Overlay
Gradient’s parameters: 
On a new layer of 4x4 px with this instrument

must be inserted this picture:

then

keep the cliché
On a new layer with 749x235 px and 72 dpi must be applied next indications: