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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 render_theming_css():
 """ Template tag that renders the needed css files for the theming app. """

    css = getattr(settings, 'ADMIN_TOOLS_THEMING_CSS', False)
    if not css:
        css = '/'.join(['admin_tools', 'css', 'theming.css'])
    return mark_safe(
        '<link rel="stylesheet" type="text/css" media="screen" href="%s" />' %
        staticfiles_storage.url(css)
    )