            // Parallax background image
                parallaxBackgroundImage: '',
                // e.g. "'https://s3.amazonaws.com/hakim-static/reveal-js/reveal-parallax-1.jpg'"

                // Parallax background size
                parallaxBackgroundSize: '', // CSS syntax, e.g. "2100px 900px"

                // Number of pixels to move the parallax background per slide
                // - Calculated automatically unless specified
                // - Set to 0 to disable movement along an axi