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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_helper(self):
 """ Add CSS links for the current page and for the plugins """

        entries = [entry for entry in self._plugin_manager.call_hook("css") if entry is not None]
        # Load javascript for the current page
        entries += self._get_ctx()["css"]
        entries = ["<link href='" + entry + "' rel='stylesheet'>" for entry in entries]
        return "\n".join(entries)