display processing in middle of current scroll position

Hi,

I am struggling with displaying processing indicator, when I have scroll X enabled . I want it to be in a middle of current scroll position.

With position: absolute; it stays at the beginning of the table, with position: fixed; it is moving with scroll bar, but when you resize table it is not in the middle of table anymore.

Here is jsFiddle: http://jsfiddle.net/vdjfq14n/

Thanks for help