I was excited for zen garden but didn’t see anything there that stood out as I was expecting more of a focus on the design rather than the css purist lens. There are some amazing things that can be done purely through css, https://a.singlediv.com/2014-2019/ comes to mind.

Not sure what the accessibility implications of (abusing?) html/css in this way are. Perhaps wrapping adding aria-role=figure would alleviate my concerns

Except that on mobile it's very not obvious how to access the themes other than dark and light, including drunk.

That's true. I did have it as a grid originally, but it pushed the content too far down. Happy to take suggestions on how to make it more obvious.

Having the horizontal scroll bar always visible and with good contrast may help (right now it auto-hides for me, Chrome on Android). Though in the initial position it may still not be obvious that it's a scroll bar...