Yeah I thinks it's usually a good idea to let the user change it. And it's not that much code really, so no issues there. If adding the toggle adds some much code that is noticeable, then you might need to rethink how you are approaching that.
Otherwise I don't see any problem for adding a toggle.
There are some people that might have the OS in light mode, but want only your site in dark mode, or vice versa. So it's always nice to give the user the option
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Yeah I thinks it's usually a good idea to let the user change it. And it's not that much code really, so no issues there. If adding the toggle adds some much code that is noticeable, then you might need to rethink how you are approaching that.
Otherwise I don't see any problem for adding a toggle.
There are some people that might have the OS in light mode, but want only your site in dark mode, or vice versa. So it's always nice to give the user the option