docs: def get_css_classes(document, style):
      """Returns CSS classes for this style.
  
      This function will check all the styles specified style is based on and return their CSS classes.
  
      :Args:
        - document (:class:`ooxml.doc.Document`): Document object
        - style (:class:`ooxml.doc.Style`): Style object
  
      :Returns:
        String representing all the CSS classes for this element.
  
      >>> get_css_classes(doc, st)
      'header1 normal'
      """
      lst = [st.lower() for st in get_all_styles(document, style)[-1:]] + \
          ['{}-fontsize'.format(st.lower()) for st in get_all_styles(document, style)[-1:]]
  
      return ' '.join(lst)