Page side part color change

In my site page https://www.pixelbox.in/contact/
you can see that the entire page is black. Is there a way that I can change the color of side part of the page keeping the mid part in black as shown in this Photoshop produced picture ?
I prefer to change it to grey. I wish to do same for all pages and if the given code acts for all pages then great.

Hi,

Try adding this CSS code to your site’s Additional CSS.

    body:not(.home) {
    	 background-color: #242424 !important;
    }
     body:not(.home) .site-header {
    	 position: static !important;
    }
     body:not(.home) .header-clone {
    	 display: none !important;
    }
     body:not(.home) #page.site, body:not(.home) .site-header {
    	 margin-left: auto;
    	 margin-right: auto;
    	 background-color: #000;
    }
     @media only screen and (min-width: 768px) {
    	 body:not(.home) #page.site, body:not(.home) .site-header {
    		 width: 750px;
    	}
    }
     @media only screen and (min-width: 992px) {
    	 body:not(.home) #page.site, body:not(.home) .site-header {
    		 width: 970px;
    	}
    }
     @media only screen and (min-width: 1200px) {
    	 body:not(.home) #page.site, body:not(.home) .site-header {
    		 width: 1170px;
    	}
    }

Regards,
Kharis
aThemes Support