Button change stylesheet

Version 3.0.3.7 default theme

Hello, I am new to this but trying to learn how to modify stuff , I have just found how to control the look of the site by modifying the stylesheet.css

What I really want to do is put a button on the top margin (next to checkout link), which says 'Dark Mode' and depending if pressed would use 1 set of stylesheet rules or another (or maybe stylesheet.css or stylesheet_2.css) ?

Thank you for any help provided, I hope it is easy enough for somebody to expain how this could be done.

You can try this ocmod extension
https://www.opencart.com/index.php?rout ... n_id=36586