Transparent outlines

transparent-outline.scss

/*
Creates a transparent outline with two colored borders around it.
  @param $transparent-width Thickness of the transparent border.
  @param $color-width Thickness of the coloured borders.
  @param $color Color of the colored borders.
*/
@mixin transparent-outline($transparent-width, $color-width, $color){
  border: $transparent-width solid transparent;
  box-shadow: 0 0 0 $color-width $color inset,
    0 0 0 $color-width $color;
}