How to Change the size of Default settings page and list page in SharePoint 2010 and change the body background color completely

Hi I was designed a master page and page layout for a branding site.  The master page having 950px width and aligned in the center.

But the problem is when I visit the default page of SharePoint like site setting, view all site content they all are remains in the same width. 

I wondered because I covered the content place holder by a div with 950px width.  But it is not applied so I decided to do a smart work.  Open the firefox and check the style with the help of firebug I found that a content table completely keep the default page there a style that take about the width and the color. 

.s4-ca {
    background: none repeat scroll 0 0 #fffff;
    margin-left: 155px;
    margin-right: 0;
    min-height: 324px;
}

I change the style as per my wish....

then paste it to my master page to override.

Now it is working....  

If you remove background color property at the time you can able to get the background color defined in the body style class..   But it is not looking fair......

Happy Coding:)