@mixin bp($break, $viewport1: null) {
  // min breakpoint
  @if $break == min {
    @media screen and (min-width: $viewport1) { @content; }
  }
  // max breakpoint
  @else if $break == max {
    @media screen and (max-width: $viewport1) { @content; }
  }
  // min & max breakpoint
  @else {
    @media screen and (min-width: $break) and (max-width: $viewport1) { @content; }
  }
}