change theme header image according to night mode vs light mode

so yea, I have a light version of my header image, and an inverted dark mode version of my sites header image, and all I want to do, is to find out how to toggle this plugins dark mode site version, and load the dark mode version of my sites header image, and load the original light mode theme header image when dark mode is turned off

I read other posts, that said to use css, and I know what css code snippets to possibly consider, but how do you feed this the appropriate css code (and more importantly WHAT file do I feed that code into respectively) in order to change the sites header image according to what device has loaded the site (for the proper resolution images accordingly) and how do you make it set the original image again (if the site defaults to loading in normal mode, not dark mode) because I’m kind of at a loss here.

https://stackoverflow.com/questions/43852116/css-background-images-in-wordpress

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