jQuery-ui slider handle with inputfield following not working when page is centered

Question

Im trying to make a input field follow the handle bar of the jQuery handle-bar. It works somehow right when using the top answer at: Jquery UI slider how to make a box follow the handler?

But it doesn't work properly when having the slider inside a container with margin:0 auto; and position:relative;

You can see what I'm talking about here

Any help or suggestions appreciated, but I really need my site to be centered.

Thanks in advance, cookies will be rewarded

Edit: I wish the input to appear below the handle-bar