* Various Mermaid improvments
- Render into iframe for improved security
- Use built-in dark theme instead of color inversion
- Remove flexbox attributes, resulting in more consistent size rendering
- Update API usage and update to latest version
* restart ci
* misc tweaks
* remove unneccesary declaration
* make it work without allow-same-origin, add loading=lazy
* remove loading attribute, does not seem to work
* rename variable
* skip roundtrip to DOM for rendering
* don't guess chart height
* update comment to make it clear it's intentional
* tweak
* replace deprecated 'scrolling' property
* remove unused css file
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
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