z-index不适用于span:before

Question

怎么把:在跨度之后？我知道我之前做过这个,但我不记得怎么做了.这是小提琴.

HTML

<span>Stack Overflow</span>

CSS

span{
background:#000;
position:relative;
color:#fff;
z-index:20;
}
span:before{
content:'';
background:#000;
position:absolute;
left:50%;
bottom:-10px;
width:20px;
height:20px;
z-index:1;
}

小提琴

Answer 1

z-index是相对的,因此:before要使伪元素出现在其父元素下面<span>,您可以指定一个z-index -1:

span:before{
    content:'';
    background:#000;
    position:absolute;
    left:50%;
    bottom:-10px;
    width:20px;
    height:20px;
    z-index:-1;
}

jsFiddle演示