I'm already constantly using "readability mode" to strip away as much of the custom styling as I can, because letting designers run riot - and building browsers that obey their wishes - has turned the web into such a mess. Tighter limits and more end-user control would be better. Different people have different preferences about their browsing experience and should be able to control that without having to rely on every last web designer to make helpful choices, because they really just don't.