code: function flipCorners(value) {
    var elements = value.split(/\s+/);
  
    if (!elements) { return value; }
  
    switch (elements.length) {
      // 5px 10px 15px 20px => 10px 5px 20px 15px
      case 4: return [elements[1], elements[0], elements[3], elements[2]].join(' ');
  
      // 5px 10px 20px => 10px 5px 10px 20px
      case 3: return [elements[1], elements[0], elements[1], elements[2]].join(' ');
  
      // 5px 10px => 10px 5px
      case 2: return [elements[1], elements[0]].join(' ');
    }
  
    return value;
  }
docs: Flip the corners of a `border-radius` value.
  
  @param {String} value Value
  @return {String}