This plugin applies to some browsers, (like Chrome on Mac/iPhone, Safari/Firefox on iPhone). For example, you could have a green header on your page or your page might have gray background color β since some browsers allow you to scroll beyond the top and bottom of the page, an awkward white background can show up beyond those edges.
You can set your page background color using an Element on the page, or an action.
Both the element and the action have an input called "Background Color." You can customize the color of the background (beyond the top and bottom of your page) by entering the hex color code in this input.