//利用背景图来画一个
//左竖线
.thin-line{
    background: -webkit-linear-gradient(left, transparent 50%, #e5e5e5 50%) no-repeat top left;
    background-size: 1px 100%;
}
//下横线
.thin-line{
    background: -webkit-linear-gradient(bottom, transparent 50%, #e5e5e5 50%) no-repeat bottom left;
    background-size: 100% 1px;
}

//利用::after伪类元素来给一个绝对定位
div::after{
    content: '';
    position: absolute;
    left: 0;
    bottom: 0;
    background: -webkit-linear-gradient(top, transparent 50%, #f2f2f2 50%) no-repeat bottom left;
    background-size: 100% 1px;
    width: 100%;
    height: 1px;
}