<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def extract_css_links(bs4):
 """Extracting css links from BeautifulSoup object :param bs4: `BeautifulSoup` :return: `list` List of links """


    links = extract_links(bs4)

    real_css = [anchor for anchor in links if anchor.endswith(('.css', '.CSS'))]

    css_link_tags = [anchor['href'] for anchor in bs4.select('link[type="text/css"]')
                     if anchor.has_attr('href')]

    return list(set(real_css+css_link_tags))