The editable sidebox works when installed and used correctly.

For the bestsellers box, add to the bottom of your stylesheet
Code:
#bestsellersContent {
    padding-bottom: 180px; 
    background: url(../images/freeshipping.gif) no-repeat bottom center;
    }
Save the image in /includes/templates/your_template/images/freeshipping.gif.

Tested and works with the absolute URL, as I can't insert the file to use the recommended relative URL.