CSS3 RGBA:

浏览器参照基准:Firefox3.6 and Later, Chrome5 and Later, Safari5 and Later, Opera10.53 and Later, IE9.0 and Later

语法:

rgba(0-255,0-255,0-255,0-1)

HEX颜色中的黑色:

background-color:#000000;

RGB颜色中的黑色:

background-color:rgb(0,0,0);

RGB颜色+opacity透明度(50%透明度的黑色):

background-color:rgb(0,0,0);
opacity:.5;

RGBA颜色(50%透明度的黑色):

background-color:rgba(0,0,0,.5);
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