text: def _css_class_list(list_of_css_classes):
      """Return list without duplicate or empty elements."""
      return filter(None, list(dict.fromkeys(list_of_css_classes)))
  
  
  def _css_class_list_string(list_of_css_classes):
      """Return string version of list without duplicate or empty elements."""
      return " ".join(_css_class_list(list_of_css_classes))
  
  
  def merge_css_classes(*args):
      """Merge CSS classes into one string."""
      css_classes = []
      for arg in args:
          css_classes += f"{arg}".split(" ")
      return _css_class_list_string(css_classes)
  