im pretty sure in most of my posts i have a screen shot xd
edit:
Actually in that same post i just linked someone says they tried to put it in the background image style and it didnt work, so your trick seems not to work always (like i suspected)
There is no need to add the class. Just put Transistors line of code in the background image of a style class xd (the }{ are the trick)
if you want it only to work when the styleclass is added you have to put
.psc-folder\/styleclassName infront and add the styleclass to the component like normal (/ of folders are changed to \/) (psc- gets added by igntion)