Can I have a URL slug make changes to one page?

Could I have one page with URL slugs that change aspects of one page, for example
website.webflow.io/dark
and it would redirect to my default page, with dark mode applied.

Sure, if your dark mode is switched on using cookies.

  • Build your light mode design as the foundation
  • Create the custom CSS needed to enact your dark mode design
  • In your site-wide head, you’d have a piece of JS that checks the cookie and if it’s dark mode time, enables your custom CSS **
  • On your /dark page, create that cookie and redirect
  • On your /light page, delete that cookie and redirect

** A lot of ways to do this, but keep it simple.
I’d probably use the script to add a class to the <body> element, like dark-mode, and then write your custom css based on that, e.g.

<style>
.dark-mode .nav {
  background-color: black;

...

Thank you for the help.
This is definitely more advanced but now I know what I need to research to make this work.