CSS - Background Image Stretch -

I'm trying to get the same background effect on this website:

By looking at this, the background of the website is black, but it is a horizontal form Increased image of the background of the page raised when the page is scrolled down, the image stays at the top but mixes in the background color.

I tried to create an image like an example and background size: cover but when I scroll down, the image remains static and only scrolls the contents if it Everything makes sense!

Looking at the example, someone please explain what CSS needs to achieve? Even more, the image should be in the shape (in PS), what should be done to spread it to large browsers without losing quality?

I tried to look at the website's CSS file to see what's going on, but it's all confusing to work on one line and working.

How do I add a link to this site to show the scroll, but apparently I do not have permission, so a screenshot must be done.

Many thanks in advance.

It looks like background CSS uses:

  Background: # 000000 url (& lt; img & gt;) No-Dual Scroll Center Top;   
 Which background color and image sets, place the image at the top, so that the background color is only visible after scrolling.  
 To see this effect, using the Chrome, change the CSS:  
  Background: # 00FF00 url (& lt; IMG & gt;) Any repeat scroll Center top;   
 And you'll see what's going on.