CSS ~ rgba example

div.qqq{
background-color:rgb(0,0,255);opacity:0.5;
}

qqqqqqqqqqqqqqqqq

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div.qqq2{
background-color:rgba(0,0,255,0.5);
}

qqqqqqqqqqqqqqqqq

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http://www.css3.info/introduction-opacity-rgba/