My site uses CSS to respect light/dark theme, so has no manual toggle. It requires Javascript and I have a personal goal to have a JS-free site, just pure HTML and CSS. I also think that a site should respect the user's own light/dark settings, and so a toggle, if one ever exists for a site, should really be a browser setting on the browser toolbar.
/u/gwern, in case you read this, your design along with Tufte.css were one of the influences of my own site: https://daveon.design/ . (Also present is inspiration from older-style publishing and manuscripts, and personal preferences. But your site was the first one -- a key influence -- I saw that inspired me with what a modern, clean personal website could be and how it could look, as well as what it might contain. It's a real honour to see you here and reply!)