Feature Request: respect mdbook theme

[xd009642]

This is reasonably self-explanatory, but there is a theme switch in mdbook and it would be super cool, if there was some way of supporting the theme, maybe by patching the svg with css for the style and allowing switching somehow or having multiple svgs for each theme and switching between them. It should probably be the case if this is done that it can either be enabled/disabled at the whole book level and at individual diagram level.

I also understand if this is too much faff for now, it feels like it may be irritating to do 😅