CSS: Circle buttons in popovers don't have checked style

### What Happened?

For stateful actions that have a toggleable state, we need a check style

### Steps to Reproduce

Test with https://github.com/elementary/dock/pull/569

### Expected Behavior

A checked style like in Quick Settings

### OS Version

8.x (Circe)

### OS Architecture

amd64 (on most hardwares)

### Session Type

Secure Session (Wayland, This is the default)

### Software Version

Latest release (I have run all updates)

### Log Output

```shell

```

### Hardware Info

_No response_