https://blog.csdn.net/leadn/article/details/78560786

.setTopLine(@c: #C7C7C7) {

  & {

    position: relative;

  }

  &:before {

    content: " ";

    position: absolute;

    left: 0;

    top: 0;

    width: 100%;

    height: 1px;

    border-top: 1px solid @c;

  }

  [data-dpr="1"] &:before {

    transform-origin: 0 0;

    transform: scaleY(0.5);

  }

}