oh shucks thanks! best of luck with coding, i didn't know anything before neocities either. there's really good html and css tutorials, and i made the lightmode switch with the help of a youtube video too <3 let me know if you need any links to guides, i'll be happy to help if i can
i made a mobile version of my site, it's actually super easy to do. i can look for links on it if you'd like, but basically the css checks screen width to see if user is on mobile or computer, and switches between the two site versions. you can see it if you crunch the window of the site on your computer, too.
Now I need to figure out where your button is :v
Ah don't worry, I don't have a button yet. Hopefully I'll make one soon, probably for my sites 1 year aniversary.