[twenty eleven] reducing background margins showing

Hi there

I am interested in reducing the amount of background ( purple area on my site) that shows on the left, right and top. I am at https://www.nadaav.com/n

Using the inspect element function I was able to identify this code controlling most of the background showing at the top:

media="screen"
html {
margin-top: 28px !important;
}

I tried adding that to my style.css and reducing the 28 to 2 but it had no effect – I wonder if I am missing some prefix to it.

I could not find any code to control how much is shown at the left and right though.

Sorry if this is me being stupid and thanks as ever.

SD