In CSS, any image path is relative to the CSS file location.
f.ex if I put the CSS file in /media/css/mystyles.css and use something like
NOTE that all the samples on this question take LAST tag occurrence, and as pointed out not supporting async loading. so if you want to do it perfect manner, you should be matching YOUR script name ADDITIONALLY. in fact scriptaculous does that.
just it's a problem that the "incomplete" code is highlighted and projects like http://areaaperta.com/nicescroll/ use that version of the code