foo.scss

@mixin adjust-font-size-to-with-border($to-size, $lines: lines-for-font-size($to-size), $from-size: $base-font-size, $border-size:0px) {
  @if not $relative-font-sizing and $from-size != $base-font-size {
    @warn "$relative-font-sizing is false but a relative font size was passed to adjust-font-size-to"; }
  font-size: $font-unit * $to-size / $from-size;
  line-height: ($font-unit * $lines * $base-line-height / $from-size) - $border-size;
}