[topic not found]
From there:
{background-image: url(URL OF OVERLAY HERE);}
Or if your image is a different size than the standard pet image:
{background-image: url(URL OF OVERLAY HERE); width: IMAGEWIDTHpx; height: IMAGEHEIGHTpx;}
[edit]I'm assuming you're talking about the kind that only shows up on their pet profile, because the paying CSC for an official overlay is something different.
This is what I have:
{background: url(link here) no-repeat; width: 0px; height: 0px; padding: 100px 100px;}
[edit]
Oops late and apparently overcomplicated ;P
Yours is basically the same, I think it just has some extra features attached that can be used if you want or not.
I just pulled from that other thread I found because I've never actually used an overlay for my pets before.