If you change this
Code:
onchange="getStyleClass('ExampleContent').style.backgroundImage = "url('<RootPath>\Images\Backgrounds\Holly.jpg')";"
To become
Code:
onchange="getStyleClass('ExampleContent').style.backgroundImage = "url('<RootPath>\Images\Backgrounds\Holly.jpg')";"
Then that won't work at all because all that the HTML will see is
Code:
onchange="getStyleClass('ExampleContent').style.backgroundImage = "
Followed by some 'unknown' text which causes an error. That is why it becomes "
Move your logic there to a function and simply call the function.