Header Section Parallax Scroll Effect jQuery And Vertical Center Margin

Question

I have a header section with a background image and a element inside with a logo.
Now this logo is centered with jQuery in the middle of the section.
When I try to add a parallax effect to the logo it's not centered anymore because I use also a margin change for the parallax.

This is my code I also added a JS Fiddle Link ( the parallax effect is not working in the editor iframe so you have to open the example in a new window.

JS Fiddle Editor
JS Fiddle Show

Code:

// Viewport Height for head section
function viewport_height() {
    var height = $(window).height();
    var viewportHeight = (50 * height) / 100;
    var viewportHeightInner = (50 * height) / 150;
    var viewportHeightInnerMargin = (50 * height) / 300;
    viewportHeight = parseInt(viewportHeight) + 'px';
    viewportHeightInnerMargin = parseInt('-' + viewportHeightInnerMargin) + 'px';
    $(".head").css('height',viewportHeight);
    $(".head .background").css('height',viewportHeight);
    $(".head .inner").css('height',viewportHeightInner);
    $(".head .inner").css('width',viewportHeightInner);
    $(".head .inner").css('margin-top',viewportHeightInnerMargin);
    $(".head .inner").css('margin-left',viewportHeightInnerMargin);
}

// Resize head section on scale
$(document).ready(function() {
    viewport_height();
    $(window).bind('resize', viewport_height);
});

// Logo Parallax scroll
$(window).scroll(function(e){
    if ($(window).width() > 800) {
        $('.head .inner').css({
            'margin-top' : +($(this).scrollTop()/2)+"px",
        });
    }
});

Answer 1

Rather than centering the green box with negative margins, try this centering method instead:

section.head .inner {
  position: relative;
  top: 50%;
  left: 50%;
  background-color: green;
  -webkit-transform:translate(-50%, -50%);
  -moz-transform:translate(-50%, -50%);
  -ms-transform:translate(-50%, -50%);
  -o-transform:translate(-50%, -50%);
  transform:translate(-50%, -50%);
}

You'll have to edit the JS to remove the negative margins. Just remove these lines:

$(".head .inner").css('margin-top',viewportHeightInnerMargin);
$(".head .inner").css('margin-left',viewportHeightInnerMargin);