Improve accessibility in the Browser Assistant popup (TAB key)

###### 💻 Browser Assistant `1.3.32 beta` on Firefox `111.0.1`.

# _:wave:_ Steps to reproduce

1. Go to either http://example.org or https://example.org;
2. Open the **Browser Assistant** popup;
3. Press TAB multiple times.

# Actual behavior

- Correct on [actions](https://user-images.githubusercontent.com/4764956/230697498-b5c025d4-4bd1-4b92-a4cd-44d6283edbcf.png) — _focus_ style is different;
- IMHO, not correct on the [toggle switch](https://user-images.githubusercontent.com/4764956/230697548-52de15af-ce56-40ab-a824-dc5ea7bd0627.png) — _focus_ style is not different.

# Expected behavior

See [this screenshot](https://user-images.githubusercontent.com/4764956/230697581-b4712b22-cc2d-4592-8679-f4b8df216340.png) for a possible adequate _focus_ style regarding the latter.

:eye: Like so we can see we are on it, just like what the AdGuard Browser extension [does](https://user-images.githubusercontent.com/4764956/230697602-a9218d57-fa07-4fc0-99db-3e5fcbbf4ce1.png) — or Firefox [does](https://user-images.githubusercontent.com/4764956/230699154-049a8c4e-469e-4634-a988-a9a0d21fb392.png).