Change container background color

Hi,

I am trying to change the container color for the page area.
See: https://www.thefuncastle.com/video-photo/

The idea is to have each page a different color, which I have done with this page, but the margins are still white.
I tried many things, but I never get just the margins area’s also in a color of choice.

Below is all my custum.css, where the #post-17 is the yellow code

.container {
position:relative;
width:1020px;
margin:0 auto;
padding:0;
float:left;
}
.container .sixteen.columns {
width: 1000px;
}
#post-17 {
background-color: #FFF550;
}