Setting Opacity in CSS For Chrome
opacity should work for chrome/safari/firefox. The -moz and -khtml syntaxes are only used to support the much older versions of these browsers.
I've never run across the -webkit-opacity style before and can't seem to find any documentation that says it exists. I would try removing it entirely or fixing the syntax bug you have in there: '-webkit-opacity:' to '-webkit-opacity' (without the trailing colon).
If that doesn't work try printing the value of opts.overlayOpacity. Make sure it's something like 0.5 and not 50 or 50%.