node_modules/clean-css/lib/optimizer/level-1/shorten-hsl.js

// HSL to RGB converter. Both methods adapted from:
// http://mjijackson.com/2008/02/rgb-to-hsl-and-rgb-to-hsv-color-model-conversion-algorithms-in-javascript

function hslToRgb(h, s, l) {
  var r, g, b;

  // normalize hue orientation b/w 0 and 360 degrees
  h = h % 360;
  if (h < 0)
    h += 360;
  h = ~~h / 360;

  if (s < 0)
    s = 0;
  else if (s > 100)
    s = 100;
  s = ~~s / 100;

  if (l < 0)
    l = 0;
  else if (l > 100)
    l = 100;
  l = ~~l / 100;

  if (s === 0) {
    r = g = b = l; // achromatic
  } else {
    var q = l < 0.5 ?
      l * (1 + s) :
      l + s - l * s;
    var p = 2 * l - q;
    r = hueToRgb(p, q, h + 1/3);
    g = hueToRgb(p, q, h);
    b = hueToRgb(p, q, h - 1/3);
  }

  return [~~(r * 255), ~~(g * 255), ~~(b * 255)];
}

function hueToRgb(p, q, t) {
  if (t < 0) t += 1;
  if (t > 1) t -= 1;
  if (t < 1/6) return p + (q - p) * 6 * t;
  if (t < 1/2) return q;
  if (t < 2/3) return p + (q - p) * (2/3 - t) * 6;
  return p;
}

function shortenHsl(hue, saturation, lightness) {
  var asRgb = hslToRgb(hue, saturation, lightness);
  var redAsHex = asRgb[0].toString(16);
  var greenAsHex = asRgb[1].toString(16);
  var blueAsHex = asRgb[2].toString(16);

  return '#' +
    ((redAsHex.length == 1 ? '0' : '') + redAsHex) +
    ((greenAsHex.length == 1 ? '0' : '') + greenAsHex) +
    ((blueAsHex.length == 1 ? '0' : '') + blueAsHex);
}

module.exports = shortenHsl;