cf. https://frontendmasters.com/blog/capo-js-a-five-minute-web-performance-boost/

https://rviscomi.github.io/capo.js/user/demo/

See https://www.htmhell.dev/adventcalendar/2022/21/

Thanks to Anthhony, I now have a better option 🙇

Using `<script>toggleTheme('dark')</script>` directly from the markdown given it's already availale from the head declaration. As a bonus, we don't mess with user's preferences for other pages.