How to Animate the Details Element

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Here’s a nice simple demo from Moritz Gießmann on animating the triangle of a <details> element, which is the affordance that tells people this thing can be opened. Animating it, then is another kind of affordance that tells people this thing is opening now.

The tricks?

  1. Turn off the default triangle: details summary::-webkit-details-marker { display:none; }. You can’t animate that one.
  2. Make a replacement triangle with the CSS border trick and a pseudo element.
  3. Animate the new triangle when the state is open: details[open] > summary::before { transform: rotate(90deg); }.

This only animates the triangle. The content inside still “snaps” open. Wanna smooth things out? Louis Hoebregts’ “How to Animate the Details Element Using WAAPI” covers that.

Here’s a fork where I’ll combine them just because:

I see Moritz put the cursor: pointer; on the summary as well like Greg Gibson suggests.