Changing HighCharts background color?

I don't really know how to do this.

I need to change background color of this highcharts chart:

http://jsfiddle.net/gh/get/jquery/1.7.2/highslide-software/highcharts.com/tree/master/samples/highcharts/demo/polar-spider/

But I don't seem to be able to do so - there doesn't seem to be any clear place to put the background color setting?

I've tried to write many different values in this section:

chart: {
        polar: true,
        type: 'line'
},

But it didn't do anything ( it occasionally broke this script ).

Do I need to change it somewhere in the included .js files? Or can it be done from the level of this loaded script?

JS is really confusing. Can anyone help me?