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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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. '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)