html css transparent background color

RGBa is the way to show a color in CSS that includes  transparency support.This allows you to fill areas with alpha opacity transparent color

 background-color:rgba(255,0,0,0.5);  

The alpha opacity parameter is a number between 0.0 and 1.0  ( 0.0 - fully transparent, 1.0 - fully opaque ) This alpha opacity parameter  supported in IE9+, Firefox, Chrome, Safari, and in Opera 10+