Responsive videos about v8.dev

[mathiasbynens]

I don't think we really need markdown-it-video; we could just add the relevant CSS, since we consistently use <figure> as wrappers around images and videos.

[mathiasbynens]

I just went through all YouTube embeds on v8.dev and confirmed they're all 16:9 (or at least, the YouTube Embed snippet for each of them outputs a 16:9-ratio'd iframe).

Note that making the videos responsive is trickier than just the examples you've highlighted, since some of our videos have <figcaption>s. Example: https://v8.dev/blog/tracing-js-dom#devtools-heap-snapshot

Our HTML is as follows (and I'd rather not add wrapper elements):

<figure>
  <iframe></iframe>
  <figcaption></figcaption>
</figure>

If we position the iframe absolutely within the figure, how do we position the figcaption correctly without knowing how many lines of text it fills up?

[mathiasbynens]

I caved and added a <div> around the <iframe> in #112. PTAL :)