Comment by pedrovhb
Nice! Seems very useful if you can drop in and have everything work.
Nitpicking a bit: it's not as much _rendering_ markdown as it's _syntax highlighting_ it. Another interesting approach there could be to use the CSS Custom Highlight API [0]. Then it wouldn't need the preview div, and perhaps it'd even be possible to have non-mono fonts and varying size text for headers.
[0] https://developer.mozilla.org/en-US/docs/Web/API/CSS_Custom_...
Can you use highlights on text area contents?