`wWebsite`'s `s_hr` snippet css targets the same element as `mass_mailing`'s `hr` snippet, resulting in interferences. This raises the speciticity of `mass_mailing.s_hr`'s css to counter that issue. X-original-commit: 112758b7c07870c5d002a87f4eed58bd8feb9bee Part-of: odoo/odoo#92138