如何找到元素与其父元素的“相对”位置？或者：如何找到蓝先生？

I have basically 2 div elements. The first is a scrolling container and the second one is an element that is placed in the container. I would like to find the y-position relative to the scrolling container. I wrapped all of it into a piece of example-code titled I have basically 2 div elements. The first is a