Is your feature request related to a problem? Please describe.
Currently Seelen-UI has no volume mixer functionality resulting in having to go to windows sound settings or using a third party app like ear trumpet through the tray bar.

Describe the solution you'd like
Include a volume mixer in the volume popup window right below master volume.

Describe alternatives you've considered
An alternative solution could be to pin Ear Trumpet app icon to the toolbar although a native solution would be preferred.

Additional context
Ear Trumpet popup example.