Cascading Style Sheets/Opacity

From WikiKnowledge

The opacity property in CSS controls how transparent an element is. The property can be set anywhere between 0.0 and 1.0. A setting of 0 means that you can see right through an element as if it wasn't there while a setting of 1 (the default) means that the element is fully opaic and you can't see through it at all.

In Internet Explorer you can use filter:alpha(opacity=x) to achieve the same results as it does not support the opacity property.