DOM tree visualizer to easily see sizing of children

Basically I want to be able to look at some kind of graphical representation of the DOM where I can clearly see which child element is affecting the size of a parent element.

Firefox had the 3D dom viewer for this but they killed it and the extension they suggest doesn't work. Chrome also has the experimental layers tool that also doesn't seem to work.

The two tools I referenced both use a layered 3d approach, but any functioning tool which easily let you visualize the children would work.