You can set the following options in the Background set of the Output Settings dialog box:

View Document As

Select Image if you want the web page to display an image or a solid color as a background behind the current image. Select Background if you want the web page to display the optimized image as a tiled background.

Background Image

Enter the location of an image file, or click Choose and select an image. The file you specify will be tiled behind the optimized image on the web page.

Color

Click the Color box, and select a background color using the color picker, or select an option from the pop‑up menu.