To change your background for your featured item follow these steps:
1. Login to your Webstore’s control panel.
2. You can only change your featured item’s background in one of these 3 templates. So make sure you selected one of these templates.
3. Go to your "Header" tab, and under your featured item tab choose the background for your featured item.
4. Click on save. Now you should be able to see your new background in your webstore!
Let me know if you have any other questions.