css利用after解决菜单栏，弹出层双阴影重叠问题

css 利用after

.custom_nav_list li:first-child:hover > a:after {
    content: '';
    background: rgb(255, 255, 255);
    position: absolute;
    height: 4px;
    width: 100%;
    bottom: 0px;
    left: 0;
    z-index: 10;
}