<i>Highest z-index was an astonishing 999999999999999999999999999 or 9.99e26. With a default key repeat on OS X, this would take 3 seconds of holding down 9 to type. If you took that many pieces of paper at .05mm thick, the stack would reach from Earth to the Sun 10 trillion times. The worst part about this large of a z-index is that a number that high will overflow and not work in the expected manner anyhow. The lowest was a more reasonable -999999.</i><p>FWIW, max z-index that is cross-browser safe is: 16777271