Well if it's my site I want to give users choice between 2 styles.
I remember Firefox used to have an option in the menu for selecting alternative stylesheets, multiple ones not just light and dark, I think it was a standard from CSS, but only Firefox had a way to select them through the UI, for other browsers you had to use Javascript to make a selector.
Thank you for illustrating the fact that the phrase "best practice" means nothing, and is little more than a synonym for "I heard this somewhere."