Spacebook comes preconfigured with the Eleventy Embed Everything which makes it very easy to embed responsive content simply by pasting the URL to your embedded content:
https://www.youtube.com/watch?v=21X5lGlDOfg
or
https://youtu.be/21X5lGlDOfg
https://twitter.com/NASA/status/1335413968299458560
See the Embed Everything docs for a full list of supported emdeds (Spotify, TikTok, Soundcloud, Vimeo, etc.)