移动端0.5px

.tab-box:after{
  content: '';
  position: absolute;
  width: 200%;
  height: 1px;
  left:0;
  bottom: 0;
  border-bottom: 1px solid #D9D9D9;
  -webkit-transform-origin: 0 0;
  transform-origin: 0 0;
  -webkit-transform: scale(.5,.5);
  transform: scale(.5,.5);
  -webkit-box-sizing: border-box;
  box-sizing: border-box
}