getBoundingClientRect() on documentElement

Click anywhere to read the documentElement’s getBoundingClientRect().left/top

1. This test is meant only for browsers that have a modern layout viewport; i.e. Chromium50+ and Edge.
2. Click anywhere to get the documentElement’s getBoundingClientRect().left/top.
3. Zoom in a bit. The fixed layer ought to move off the screen.
4. Scroll all the way down to the end of the page, then up until the fixed layer "top left" becomes visible. Click anywhere again.

Top left of layout viewport