CSS hover如何作用在伪元素before上

使用方法如下：

&::before {
    content: '';
    position: absolute;
    bottom: 0;
    width: 100%;
    border-bottom: 1px solid $line-color;
    transform: scale(0);
    transition: all .5s;
}
&:hover::before {
    transform: scale(1);
}