okay, I just realized it's the rule from the building blocks, so we must use the same id and href to trigger :target, so the "tab" prefix is fine. But will it be simpler to use without "tab" prefix for both id of li and href of a? then we can use the "tabs" prefix for the id of a and the JS code in https://github.com/mozilla-b2g/gaia/pull/9491/files#L1L1559 doesn't need to be changed.