text: (function(){
  
    var parallax = document.querySelectorAll(".parallax"),
        speed = 0.5;
  
    window.onscroll = function(){
      [].slice.call(parallax).forEach(function(el,i){
  
        var windowYOffset = window.pageYOffset,
            elBackgrounPos = "0 " + (windowYOffset * speed) + "px";
        
        el.style.backgroundPosition = elBackgrounPos;
  
      });
    };
  
  })();