Improvements for the dropdown chevrons

[amotl]

@msbt suggested at crate/crate-docs-theme#417 (comment):

Quick question about the chevrons you're using for up/down: Wouldn't it be nicer to have only one that turns 180° when you open it instead of two that show/hided depending on the status?

Like

details.sd-dropdown .sd-summary-down {
  transition: 180ms;
}

details.sd-dropdown[open] > .sd-summary-title .sd-summary-down {
  /* visibility: hidden; */
  transform: rotate(-180deg);
}

[amotl]

Dear @msbt,

thanks for your suggestion. A proposal for an adjustment like this should probably be directed to https://github.com/executablebooks/sphinx-design instead.

With kind regards,
Andreas.

[msbt]

@amotl ah alright, I thought that was your thing 😀

[amotl]

Dear Matthias,

this humble repository is just building upon the excellent work by @chrisjsewell and contributors on behalf of sphinx-design, whom all credits are due. Unfortunately, I've not made it in time to reach out to them properly yet, and now I am kind of heading to the beaches already. I hope to be able to do it properly after vacation.

With kind regards,
Andreas.