Test overlap is rendered correctly when hovering over elements

Case 1, original layer tree: 

    Case 2: hovering over the "middle" element (causes that div to become its own composited layer)
    

    Case 3: hovering over the "middle2" element (causes that div to become its own composited layer)
    

    Case 4: hovering over the "top" element (causes that div to become its own composited layer)
    

    Case 5: back to situation in case 1