While browsing themes in theme selector, the currently active theme will
always be marked with a check icon so you can always have a reference of
where you started from.

Self-Review Checklist:

- [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)
- [ ] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Here's a preview: 
<img width="950" height="806" alt="Screenshot 2026-06-03 at 13 09 46"
src="https://github.com/user-attachments/assets/2081d9ec-b56d-4542-be58-e59e3569bc7a"
/>
<img width="958" height="818" alt="Screenshot 2026-06-03 at 13 09 52"
src="https://github.com/user-attachments/assets/134d933f-c9de-4b2c-80f5-ed5be4fb2844"
/>


Release Notes:

- Improved the theme and icon selectors to display a check next to the
active theme

---------

Co-authored-by: dino <dinojoaocosta@gmail.com>