Simple Parallax using jquery

simple-parallax.css

.parallax {
  background-image: url('http://via.placeholder.com/1600x800');
  background-position: top center;
  background-repeat: no-repeat;
  background-size: 100% auto;
}

simple-parallax.js

$(function() {
    
    var 
      $el = $('.parallax'), // trigger element
      $scrollWrap = $('window'), // scroll element 
      speed = 0.05; // speed animation
    
    function parallax(){
      var scroll = $scrollWrap.scrollTop();
      $el.css({
        'background-position':'50% '+(speed*scroll)+'px'
      });
    };
    
    $scrollWrap.on("scroll", parallax);
  
});