[Bug]: Sidebar dropdown does not close when the arrow is clicked again

Summary

In the left sidebar navigation, when a section with sub-items is expanded (for example, "Installation"), clicking its downward-facing arrow again does not collapse the section. Users naturally expect an expand/collapse toggle arrow to work in both directions — even if this is intentional (e.g., to keep the active page's context visible), it hurts the UX since users assume clicking again will close the dropdown.

Page

https://react.dev/learn/installation

Details

To Reproduce

1. Go to any documentation page with an expanded sidebar section, such as https://react.dev/learn/installation.
2. Locate the left sidebar navigation.
3. Click on the downward-facing arrow next to the currently active/expanded section (e.g., "Installation").
4. Notice that the section does not collapse as expected.

Expected behavior
Clicking the dropdown arrow of an already expanded section should toggle it back to a collapsed state.

Desktop:

• OS: Windows
• Browser: Chrome

Additional context
Observed on the main react.dev documentation site. Fixing this would make the navigation feel more intuitive and aligned with standard UI patterns for accordions/dropdowns.

Commencez par la barre latérale de https://react.dev/learn/installation et suivez le gestionnaire de clic associé à la flèche de la section dépliée sur le site de documentation. Reproduisez le comportement dans Chrome, puis vérifiez qu’un nouveau clic sur la flèche replie la section, tout en maintenant le fonctionnement de la navigation et du contexte de la page active.