The background is what shows up behind everything else, including the dashboard, the toolbar, and all of your widgets. These settings let you customize how the background looks. To get here, in the settings, click on the "Background" button in the navigation.
This type lets you fill the background with a solid color.
This type lets you fill the background with a linear gradient.
This type lets you set the background to an image. Once it is selected, use the File Input to add an image.
This type lets you set the background to a video. Once it is selected, use the File Input to add a video. When specifying the URL, it needs to directly link to a video file; an MP4, WebM, or Ogg file; not a video streamer like YouTube (see below for a YouTube background).
This type lets you set the background to an IFrame (which lets you render other websites as the background). Once it is selected, use the File Input to add an HTML file or link to a website. Keep in mind, that some websites block their pages from being used in IFrames.
This type plays a YouTube video in the background. Just put in the video's id or page URL. This only works for videos that allow embedding.