To me the difference is that Svelte is a lot more pure JavaScript than Vue. I haven't had the chance to use it in any larger project, but in my small playgrounds, I've definitely enjoyed it more than Vue.
Viewing the source shows an html page without a closing body nor html tag: it's probably not the best case for showcasing it seems.
The layout it all over the place too using FFox, (it's fine on Chrome and Safari) so it also seems to be lacking in some basic cross browser testing, which again, is not good news when show-casing a framework, as a frameworks' prime responsibility is to ensure cross browser/platform uniformity.
Hopefully this all boils down to a simple 'oopsie' in your project, rather than svelte.
> Viewing the source shows an html page without a closing body nor html tag
It's actually not required to close those tags, the browser will interpret them correctly. (You can see this when inspecting the elements on the page, not just the raw source)
I’m glad to see Svelte growing in popularity here.