Open a new file with
780x148 px and
72 dpi. Paint it in
464646.

Having this instrument

it’s possible to represent the lowest layer of the central panel of the site’s header.
Blending Options-Gradient Overlay
Gradient’s parameters:
Blending Options-Stroke
Gradient’s parameters: 
Now you should choose the instrument

to create the inside panel’s space colored in black.
Blending Options-Outer Glow