1px细线

.bordert1px {
    position: relative;
}
.bordert1px:before {
    content: " ";
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 1px;
    background-color: #d8d8d8;
    -webkit-transform-origin: 0 0;
    transform-origin: 0 0;
    -webkit-transform: scaleY(0.5); 
    transform: scaleY(0.5); // 纵向缩放
}

.rec-app-content{
    position: relative;
}
.rec-app-content::after {
    position: absolute;
    content: '';
    top: 0;
    left: 0;
    width: 300%;
    height: 300%;
    transform-origin: 0 0;
    transform: scale(.3333);
    pointer-events: none;
    border-bottom: 1px solid #c1c1c1;
}

<div class="line-bottom"></div>

.line-bottom {
  background-image: url(~assets/img/line-bottom.png);
  background-size: 100% 1px;
  background-repeat: no-repeat;
  background-position: bottom;
}