Hi sandraholt,
Your WordPress theme is built on the 960 grid, with the original intention of being responsive. That said, it seems that your site has a number fixed widths thrown in there, so I don’t think that adding some more will be an issue.
In your wrapper definition in style.css on line 26 does not define a width so the file 960.css is setting it. To make “less background” you will want to add the following code to your style.css file after the rule that starts on line 26 ends:
.container_12, .container_16{
width: 1000px;
}
You will also need to add a background color to your banner under the rule #sub-header
that starts on line. Something like background-color: #00000;
where #000000 is the hex number for the color you want to use.
I assume that you will also want to make your content column larger, so you will also want to add width: 660px
to style.css in the rule that starts on line 42. You want the change in width of this column to be equal to the change in .container_12, .container_16
.
I hope that this helps.