The last properties in the CSS fail CSS3 validation: .anythingSlider .start-stop { transition-duration: 0; -o-transition-duration: 0; -moz-transition-duration: 0; -webkit-transition-duration: 0; } Easy fix to this is to add a a seconds indicator to the duration: .anythingSlider .start-stop { transition-duration: 0s; -o-transition-duration: 0s; -moz-transition-duration: 0s; -webkit-transition-duration: 0s; }