移动端1px细线

border-bottom-1px($c)  position relative  &::before    content ''    display block    position absolute    left 0    right 0    bottom 0    height 1px    background-color $c    @media only screen and (-webkit-device-pixel-ratio:2)      transform scaleY(.5)    @media only screen and (-webkit-device-pixel-ratio:3)      transform scaleY(.3333333)