(CSS) Make a background image scroll slower than everything else

I know this is very late, but I wondered wether it would not be working easier than the codes above and invested 15 mins of my live.
Here is my code:

document.getElementById("body").onscroll = function myFunction() {  
    var scrolltotop = document.scrollingElement.scrollTop;
    var target = document.getElementById("main1");
    var xvalue = "center";
    var factor = 0.5;
    var yvalue = scrolltotop * factor;
    target.style.backgroundPosition = xvalue + " " + yvalue + "px";
  }
#main1 {
    background-image: url(https://images.unsplash.com/photo-1506104489822-562ca25152fe?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9);
    background-position: top center;
    background-attachment:scroll;
    background-size: cover;
    height: 80vh;
    width: 100%;
}
#placeholdersoyoucanscroll{
    height:100vh
}
<body id="body">
      <main>
        <div id="main1">
        </div>
        <div id="placeholdersoyoucanscroll">
        </div>
    </main>
</body>

you can use something simple like here: html:

Motion

css:

body {

  min-height:4000px;
  background-image: url("http://www.socialgalleryplugin.com/wp-content/uploads/2012/12/social-gallery-example-source-unknown-025.jpg");
}

h1 {margin-top:300px;}

js:

(function(){

  var parallax = document.querySelectorAll("body"),
      speed = 0.5;

  window.onscroll = function(){
    [].slice.call(parallax).forEach(function(el,i){

      var windowYOffset = window.pageYOffset,
          elBackgrounPos = "50% " + (windowYOffset * speed) + "px";

      el.style.backgroundPosition = elBackgrounPos;

    });
  };

})();

Here is jsfiddle


I stumbled upon this looking for more flexibility in my parallax speed that I have created with pure CSS and I just want to point out that all these people are wrong and it is possible with pure CSS It is also possible to control the height of your element better.

You will probably have to edit your DOM/HTML a bit to have some container elements, in your case you are applying the background to the body which will restrict you a lot and doesn't seem like a good idea.

http://keithclark.co.uk/articles/pure-css-parallax-websites/

Here is how you control the height with Viewport-percentage lenghts based on screen size:

https://stanhub.com/how-to-make-div-element-100-height-of-browser-window-using-css-only/

  .forefront-element {
    -webkit-transform: translateZ(999px) scale(.7);
    transform: translateZ(999px) scale(.7);
    z-index: 1;
  }

  .base-element {
    -webkit-transform: translateZ(0);
    transform: translateZ(0);
    z-index: 4;
  }

  .background-element {
    -webkit-transform: translateZ(-999px) scale(2);
    transform: translateZ(-999px) scale(2);
    z-index: 3;
  }

Layer speed is controlled by a combination of the perspective and the Z translation values. Elements with negative Z values will scroll slower than those with a positive value. The further the value is from 0 the more pronounced the parallax effect (i.e. translateZ(-10px) will scroll slower than translateZ(-1px)).

Here is a demo I found with a google search because I know there are a lot of non-believers out there, never say impossible:

http://keithclark.co.uk/articles/pure-css-parallax-websites/demo3/