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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 css_files(self):
        ''' The CSS files in the BokehJS directory.

        '''
        bokehjsdir = self.bokehjsdir()
        js_files = []
        for root, dirnames, files in os.walk(bokehjsdir):
            for fname in files:
                if fname.endswith(".css"):
                    js_files.append(join(root, fname))
        return js_files