Fluid header with fixed navbar and background

[Angle4cor]

Hi. For few days now I'm looking for the solution of my problem with postion of my header, navbar and background. I want to make my header width for all screen, navbar stays normal like in fixed style and my background to be fixed, but when I would scroll the page down, the background would change into some color.
English is not my national language and its really hard for me to explain this for you and I'm sure its way too harder for you to understand what I have writen here as well, but at least I tried.

Simple put - I want to get something like this - xboxforum.pl I'm not sure, but probably I shouldnt put here this link, but otherwise I cant explain correct what exactly I need to do with the background. So sorry in advance for that.

Sorry for my english. Any help will be greatly appreciate.

I'm using vB 4.1.7 and my style is breezefixed - https://vborg.vbsupport.ru/showthread.php?t=233455