sidebar: Add some small design tweaks (#51936)

- [x] I've reviewed my own diff for quality, security, and reliability
- [X] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- N/A
d934ba6ceaDanilo Leal committed on 3/19/2026, 2:15:24 PM· committed by GitHubparent735eb43
3 files changedLine totals unavailable