It was all built in-house by me and other members of the Svelte community. The playground widget is technically a standalone thing, but it wasn't totally design

It was all built in-house by me and other members of the Svelte community. The playground widget is technically a standalone thing, but it wasn't totally designed to be used outside https://svelte.dev https://svelte.dev so may be a bit warty! https://github.com/sveltejs/svelte-repl https://github.com/sveltejs/svelte-repl (the code for the site itself is in the main project repo https://github.com/sveltejs/svelte/tree/master/site https://github.com/sveltejs/svelte/tree/master/site)