透明兼容写法

  针对IE透明写法

-ms-filter:”progid:DXImageTransform.Microsoft.Alpha(Opacity=50)”; 
filter: alpha(opacity=50); 

  opacity透明兼容所有浏览器写法

若有背景色background-color与文本内容存在情况下，应用下面样式后背景色background-color与文本内容都透明

    /* older safari/Chrome browsers */  
    -webkit-opacity: 0.5;  
    /* Netscape and Older than Firefox 0.9 */  
    -moz-opacity: 0.5;  
    /* Safari 1.x (pre WebKit!) 老式khtml内核的Safari浏览器*/  
    -khtml-opacity: 0.5;  
    /* IE9 + etc...modern browsers */  
    opacity: .5;  
    /* IE 4-9 */  
    filter:alpha(opacity=50);  
    /*This works in IE 8 & 9 too*/  
    -ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";  
    /*IE4-IE9*/  
    filter:progid:DXImageTransform.Microsoft.Alpha(Opacity=50);  

  只针对背景透明

非IE：background:rgba(0,0,0,0.5);
IE：filter:progid:DXImageTransform.Microsoft.gradient(startColorstr=#7f000000,endColorstr=#7f000000);

 startColorStr、endColorstr:设置或检索色彩渐变的开始颜色和透明度。其中startColorstr=#7f000000  7f是透明度十六进制值，000000颜色值

【资料参考】 

http://caniuse.com/#feat=css-opacity

https://developer.mozilla.org/en-US/docs/Web/CSS/opacity?redirectlocale=en-US&redirectslug=CSS%2Fopacity

http://blog.csdn.net/freshlover/article/details/17143341