Collapsible Admonitions

[janbaum]

Problem

Would be nice to have collapsible admonitions :) Personally I like to hide technical details in them, so the page is cleaner overall.

I am aware of mdbook-admonish and using it, but since it is not compatible with mdbook 0.5
I would like to use the integrated features instead.

Proposed Solution

Use - to mark an admonition as collapsible, like:

> [!NOTE]-
> General information or additional context.

Notes

With that, custom headers (#2975) and the possibility to add custum admonitions with css like in mdbook-admonish would make it feature complete for me.