请教背景透明设置，这样写到底是透明度多少？

[zeo]

#tf-home .overlay{
background: -moz-linear-gradient(top, rgba(0,0,0,0.8) 0%, rgba(0,0,0,0.73) 17%, rgba(0,0,0,0.66) 35%, rgba(0,0,0,0.55) 62%, rgba(0,0,0,0.4) 100%); /* FF3.6+ */
background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,rgba(0,0,0,0.8)), color-stop(17%,rgba(0,0,0,0.73)), color-stop(35%,rgba(0,0,0,0.66)), color-stop(62%,rgba(0,0,0,0.55)), color-stop(100%,rgba(0,0,0,0.4))); /* Chrome,Safari4+ */
background: -webkit-linear-gradient(top, rgba(0,0,0,0.8) 0%,rgba(0,0,0,0.73) 17%,rgba(0,0,0,0.66) 35%,rgba(0,0,0,0.55) 62%,rgba(0,0,0,0.4) 100%); /* Chrome10+,Safari5.1+ */
background: -o-linear-gradient(top, rgba(0,0,0,0.8) 0%,rgba(0,0,0,0.73) 17%,rgba(0,0,0,0.66) 35%,rgba(0,0,0,0.55) 62%,rgba(0,0,0,0.4) 100%); /* Opera 11.10+ */
background: -ms-linear-gradient(top, rgba(0,0,0,0.8) 0%,rgba(0,0,0,0.73) 17%,rgba(0,0,0,0.66) 35%,rgba(0,0,0,0.55) 62%,rgba(0,0,0,0.4) 100%); /* IE10+ */
background: linear-gradient(to bottom, rgba(0,0,0,0.8) 0%,rgba(0,0,0,0.73) 17%,rgba(0,0,0,0.66) 35%,rgba(0,0,0,0.55) 62%,rgba(0,0,0,0.4) 100%); /* W3C */
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#cc000000', endColorstr='#66000000',GradientType=0 ); /* IE6-9 */
height: auto;
background-attachment: fixed;

[it407841482]

顶部黑色.8 ，底部黑色.4 ，上下颜色线性变化，其他都是浏览器兼容