This example has been put together to exhibit Opera's support for CSS 3 opacity. This page is a simple page with 2 <div>s, one absolutely positioned over the other, but given opacity so you can see this one underneath it. The CSS that styles this is as follows:
body {
font-family:georgia, serif;
font-size: 80%;
}
#explanation {
  width: 400px;
}
#nonsense {
  position: absolute;
  left: 150px;
  top: 50px;
  background-color: hsl(240, 100%, 50%);
  Opacity: 0.85;
  width: 200px;
  padding: 5px;
}
#lighter {
  background-color: hsl(240, 100%, 60%);
}
Wow - I'm still transparent, and now my background colour is being defined using an HSL colour value too!
This is a second paragraph, in which I easily created a lighter shade by simply increasing the lightness value.