RGBA stands for Red Green Blue Alpha. It is an extension of CSS2, Alpha specifies the opacity of a color and parameter number is numerical between 0.0 to 1.0.
Example
The following example shows rgba color property −
<html>
<head>
<style>
#p1 {background-color:rgba(255,0,0,0.3);}
#p2 {background-color:rgba(0,255,0,0.3);}
#p3 {background-color:rgba(0,0,255,0.3);}
</style>
</head>
<body>
<p>RGBA colors:</p>
<p id = "p1">Red</p>
<p id = "p2">Green</p>
<p id = "p3">Blue</p>
</body>
</html>