Mitch, instead of using your script, add this to the "Extra Properties" section of the Style you want to turn upside-down.

Code
body {
    width: 100%;
    height: 100%;
    -moz-transform: rotate(180deg);
    -webkit-transform: rotate(180deg);
    -ms-transform: rotate(180deg);
    -o-transform: rotate(180deg);
    transform: rotate(180deg);
}

This will allow users to turn OFF the upside-down by selecting a different style.
You could also just duplicate your main style, add this to it and call it "main upside-down" or whatever. Then set that as the default style for the day smile dont forget to reset your default style to the correct one when you're done having fun.

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