Fix for CSS opacity in Internet Explorer

How to set CSS opacity in Internet Explorer? It's easy for good browsers like Firefox, Google Chrome or new IE9:

opacity: 0.5;

For old Safary versions you probably also need

-khtml-opacity: 0.5;

For IE6, IE7 you can write

filter: alpha(opacity=50);

and for IE8

-ms-filter: "alpha(opacity=50)";

Saidly, but filter with opacity value in IE isn't enough. Element should be positioned, in order that opacity would work in IE. If the element doesn't have a position, there is a little trick in order to get it working. Add 'zoom: 1' to your CSS.

filter: alpha(opacity=50);        // IE6, IE7
-ms-filter: "alpha(opacity=50)"; // IE8
zoom: 1;

I have faced this problem with Schedule component in PrimeFaces. The button "today" is not disabled in IE7 for the current day although it has the jQuery UI style .ui-state-disabled. The fix would be

/* IE7 hack */
div.fc-button-today.ui-state-disabled {
    *zoom: 1;
}

* means the style is applied for IE7 only.