css div transparent

hi,
i introduce a new technology in css that is making div tag as transparent looking in better

<div id="demo">
</div>
the css code will be given by,

#demo{

opacity:0.9;

filter:alpha(opacity=60); /* For IE8 and earlier */

position:absolute;
color:#0000FF;
background: #000000;
border:1px solid #111111;
}
opacity gives the transparent property
thank you.