ynw/style/mobile.scss

.border {
  position: relative;
}
.border::after {
  position: absolute;
  content: " ";
  top: -50%;
  right: -50%;
  bottom: -50%;
  left: -50%;
  transform: scale(0.5);
}

@mixin thin-border($color) {
  @extend .border;
  border-bottom: 1px solid $color;
}