# img 设置伪类无效

[Shenchuanhuan]

给img标签设置伪类，并不会生效。
对比如下：

<div class='testDiv'></div>
<img class='testImg' />

.testDiv {
    position: relative;
    width: 50px;
    height: 50px;
    background-color: black;
}
.testDiv:after {
    content: '';
    position: absolute;
    width: 20px;
    height: 20px;
    background-color: green;
}
.testImg {
    position: relative;
    left: 100px;
    width: 50px;
    height: 50px;
    background-color: black;
}
.testImg:after {
    content: '';
    position: absolute;
    width: 20px;
    height: 20px;
    background-color: green;
}