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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 add_css(self, subdir, file_name_prefix):
 """Add a css file for this resource. If self.minify is True, checks if the .min.css file exists. If not, falls back to non-minified file. If that file also doesn't exist, IOError is raised. Positional arguments: subdir -- sub directory name under the resource's main directory (e.g. css or js, or an empty string). file_name_prefix -- file name without the file extension. """

        suffix_maxify = '.css'
        suffix_minify = '.min.css'
        if self.minify and self.file_exists(subdir, file_name_prefix, suffix_minify):
            self.resources_css.append(posixpath.join(self.DIR, subdir, file_name_prefix + suffix_minify))
        elif self.file_exists(subdir, file_name_prefix, suffix_maxify):
            self.resources_css.append(posixpath.join(self.DIR, subdir, file_name_prefix + suffix_maxify))
        else:
            file_path = os.path.join(self.STATIC_DIR, self.DIR, subdir, file_name_prefix + suffix_maxify)
            raise IOError('Resource file not found: {0}'.format(file_path))