Discuss down-up chevron animation with Sphinx Design upstream

[agriyakhetarpal]

Eventually, we synced up on this outside of GitHub and decided that we'll keep parity with the Sphinx Design components: the open-by-default dropdown can stay (even if we may think it's wrong), and we'll drop the 180-degree animation for the case where the chevron rotates from a down position to an up position, as Sphinx Design does not animate that right now.

I'll open a new issue in the Sphinx Design issue tracker to ask for their opinions on adding this 180-degree animation, and then we can decide to bring this back here based on their response, and when (if) they implement it.

Originally posted by @agriyakhetarpal in #675 (comment)