There probably should be a toggle or a separate brightness control (i.e. "maximum brightness" and "default brightness") if something like that is exposed to the

There probably should be a toggle or a separate brightness control (i.e. "maximum brightness" and "default brightness") if something like that is exposed to the web. Letting content be arbitrarily much brighter than what the user expects seems a terrible design, easily exploitable by advertisers and all sorts of attention thieves.