I would like the following two volume control features added to Osu!, please. 
1) The ability to adjust the music and effect volume control levels during a game, instead of having to go to the options menu each time to adjust them. To change the music and effect volume control levels, we could use the mouse wheel in combination with the Ctrl, Shift and Alt keys. Or we could hold down the left, or right mouse buttons whilst turning the mouse wheel, etc.
2) An OSD for the master, music and effect volume control levels, that appears on the screen for a short amount of time whilst adjusting the levels with the mouse wheel during a game.
1) The ability to adjust the music and effect volume control levels during a game, instead of having to go to the options menu each time to adjust them. To change the music and effect volume control levels, we could use the mouse wheel in combination with the Ctrl, Shift and Alt keys. Or we could hold down the left, or right mouse buttons whilst turning the mouse wheel, etc.
2) An OSD for the master, music and effect volume control levels, that appears on the screen for a short amount of time whilst adjusting the levels with the mouse wheel during a game.