Access this element's content position.
This returns a rectangle with the dimenions actually available for content in this element, in pixels, regardless of this element's box-sizing property. Unlike getBoundingClientRect, the dimensions of this rectangle will return the same numerical height if the element is hidden or not.
Important note: use of this method will perform CSS calculations that can trigger a browser reflow. Therefore, use of this property during an animation frame is discouraged. See also: Browser Reflow