Question

I am trying to set the transparency of a table background color. But when I write this code in CSS it shows me the error “Validation (CSS2.1): filter is not a known property name”
and the same error for opacity.

Why is this so?

.semiTransparent 
{ 
 filter: alpha(opacity = 50);
 opacity: 0.5;
}

Answer 1

Css filter is IE-specific. If you don’t use color: rgba(r,g,b,a); where a is alpha channel responsible for transparency, you must use a few improper css properties to have semi-transparent object in all browsers.

.semiTransparent {
    filter:alpha(opacity=50);
    -moz-opacity:0.5;
    -khtml-opacity: 0.5;
    opacity: 0.5;
}

Above code works in all browsers, but is invalid.