Reader Interface. Enables you to select between two reader interface designs for your book, Scalar 1 and Scalar 2. Enable the display of navigation buttons in margins.
Thumbnail image. The thumbnail that will appear next to your book's title on the Scalar Index page. Upload an image using the "Choose File" button.
Background image. To change your book's background, you must first import the image you want to use into Scalar; then it can be selected in the drop-down menu here.
Custom style. This field accepts CSS code, which will be applied across the whole book, superseded only by that set for an individual page.