I want to leave this up to design whether and how we fix this

I'm not sure if we can do that better by touching just the arrow, but as generally the full header of the admonition is clickable, I think this should be something similar to the tabs and underline the title on hover.

an alternative is that the arrow rotate on click depending on wether the detail is expanded or not, we could rotate the arrow on hover instead:

details.sd-dropdown>.sd-summary-title:hover .sd-summary-chevron-right {
    transform: rotate(90deg);
}

details.sd-dropdown[open]>.sd-summary-title .sd-summary-chevron-right {
    transform: rotate(0deg);
}

details.sd-dropdown[open]>.sd-summary-title:hover .sd-summary-chevron-right {
    transform: rotate(-90deg);
}

Thanks @Carreau, those are excellent suggestions and I thought the same. Here are the updated designs:

Figma link to component

🎥 Video preview:

Figma - Admonitions 📝 - Hover Effect - Watch Video

I am +1 on these more visible designs

Some thoughts that came out of today's team call:

• Consistency among the different types of admonitions in the theme is key (Sphinx Design, Sphinx-togglebutton)
• Just darkening on hover is not enough. But text underline should be enough of a hover effect (Click to expand / Click to collapse).
• If we cannot add the expand/collapse text easily to the Sphinx Design admonitions, we could just underline the chevron icon and call it a day.
• Be wary of adding the expand/collapse text via ::before or ::after pseudo-elements. Creates a problem for translatable strings. May also create an accessibility problem: is the pseudo-element text available to screen readers?

Is this still in design? My take is that between the design frames, the discussion and the notes on this issue it's ready to be picked up by dev (me). Am I right or am I wrong?

Thanks for the bump @gabalafou, I missed your last comment.

If we cannot add the expand/collapse text easily to the Sphinx Design admonitions, we could just underline the chevron icon and call it a day.

I can create a hover effect for just the icon if we cannot add text easily, just let me know. I'm personally not in favour of underlining icons 🙈

Other than that, you're right about the issue status, this is ready for dev!