bootstrap-italia/src/scss/_functions.scss

// Custom functions (not available in Bootstrap)
@function hsb($h-hsb, $s-hsb, $b-hsb) {
  // Checking hsb values for 0 and turning them into 1 to avoid issues with SASS compiler
  @if $h-hsb < 1 {
    $h-hsb: 1;
  }
  @if $s-hsb < 1 {
    $s-hsb: 1;
  }
  @if $b-hsb < 1 {
    $b-hsb: 1;
  }

  @if $b-hsb < 1 {
    @return hsl(0, 0%, 0%);
  } @else {
    $l-hsl: calc($b-hsb / 2) * (2 - calc($s-hsb / 100));
    $s-hsl: calc(($b-hsb * $s-hsb) / if($l-hsl < 50, $l-hsl * 2, 200 - $l-hsl * 2));
    @return hsl($h-hsb, $s-hsl * 1%, $l-hsl * 1%);
  }
}

@function hsb-with-brightness-modifier($h-hsb, $s-hsb, $b-hsb, $b-variant) {
  $b-hsb: $b-hsb + $b-variant;
  @return hsb($h-hsb, $s-hsb, $b-hsb);
}

@function color-hover($color) {
  @return desaturate(shade-color($color, 10%), 10%);
}

@function url-friendly-color($color) {
  @if str-slice('#{$color}', 1, 1) == '#' {
    @return '%23' + str-slice('#{$color}', 2, -1);
  } @else {
    @return $color;
  }
}