Export as Image doesn't work in dark mode

[menghif]

"Export as Image" doesn't include text when exported from dark mode:

[rjwignar]

I think this is because in dark mode the body text is white and camouflages into the white background. I modified the text to red using my browser's dev tools and was able to get the text to appear:

I haven't verified this, but I think the white text in the code blocks and rendered diagrams are unaffected by virtue of being in their own subcomponents.

[rjwignar]

I might be wrong, but it seems the handler takes a screenshot of the message CardBody. I wonder if capturing the entire Card instead would fix this issue (so the text would be visible in its respective background)