The option to switch between a light and a dark theme is getting more and more popular.
However, every site implements this feature differently. It could be useful for power users to have a global option in the browser to switch between light and dark themes which gets applied to all websites.
As far as I know there is no standard (tag, attribute, handler, css-attribute, etc.) which would define such a behavior. Even if there isn't, is there a convention between web developers which is similar to this?