DIV透明度设置

<div id="Layer1" style="position:absolute; 200px; height:115px; left:50px;top:50px;filter:alpha(opacity=30);opacity: 0.6;background-color:blue"></div>

opacity值越大，透明度越高

FF
<script>document.getElementByIdx_xx_x("Layer1").style.opacity = "0.3";</script>

IE
<script>document.getElementByIdx_xx_x("Layer1").style.filter = "alpha(opacity=30)";</script>