Adding themes to website

[Alan Treecko]

I have this website that I wanna have changeable themes like this website, however, I don't know how to start.
I think some websites use swapped CSSes as different themes, however, mine's is a completely different page.
I heard using cookies is good to use.

 

[rikumax25!]

What do you mean by different page

 

[Alan Treecko]

When a different theme is selected, it goes to a different version of that page with the theme.

 

[vinstage]

Have you tried YouTube, or perhaps looking around the tool you're using to create your website?