Confusing icon for mute buttons
In the Volume Levels list, every entry contains a slider and a mute button.
The mute buttons are using the "audio-volume-muted-symbolic" image and using the state of the button to indicate the action: toggled -> muted, not toggled -> not muted.
Instead, I think it would be clear to map:
- muted -> toggled AND use "audio-volume-muted-symbolic"
- not muted -> not toggled AND use "audio-volume-hight-symbolic"