css background transparent

i need to create a pop up window in css which opens wh开发者_运维百科en we click a button or anything else. when that screen was open it should be a transparent one, so that the background text or images to that screen should be a viewable one when it was open(look like glass or mirror)....

In jQuery i use "Dialog" and modified css as below :

.ui-dialog { opacity: 0.9; }

or see jQuery UI dialog overlay

Use a semi-transparent png (including alpha) as the background image of your 'popup'.

.popup {
 background-image: url(images/SemiTransparentImageWithAlphaChannel.png);
}

Which works pretty much cross-browser (no IE6) and doesn't need CSS3