Modal Popup Style opacity

Hey guys n gals,

In the SampleWebSite that came with the AJAX Control ToolKit the stlying for the modalBackgroud looks like this.

/*Modal Popup*/

.modalBackground {

background-color:Gray;

filter:alpha(opacity=70);

opacity:0.7;

}

I was wondering if anyone could tell me what theopacity:0.7; Portion of this style does? Take this Element out of the style and it has no visual effect on the page. The reason i am asking this is becuase thefilter:alpha(opacity=70); Portion is causing me abnormal side effects on a completly unrelated control ( at least to my junior eyes )

The side effect involves a GridView which i have setup to have a Frozen header and a onscroll event for saving the position of the scrollbar. The actual side effect occurs on a postback which shifts the frozen header above where it was initialy appearing like it is floating off the grid.

In any case, I would like to know what theopacity:0.7; Does as i need to find an alternative to thefilter:alpha(opacity=70);

Regards,

Michael

Okay so opacity isnt supported in IE7, nor colour: rgba...