Media elements from third party sites are not loaded. This happens in (non-exhaustive list)

• https://learn.svelte.dev/tutorial/optional-slots
• https://learn.svelte.dev/tutorial/media-elements
• https://learn.svelte.dev/tutorial/onmount
• https://learn.svelte.dev/tutorial/sharing-code

Not sure why - I'm guessing because the web container behaves as if it's a localhost instance running without https, and the sites then refuse to answer.