Can't get Theme to apply on UDListItem

I have tried everything I can change the color on MuiSvgIcon for NewUDListItem by adding the following around UDList:

New-UDList -Dense -Content {
  New-UDStyle -Content {
    New-UDListItem -Label 'Windows' -Icon (New-UDIcon -Icon Windows -Size xs -Solid) -Children {
      New-UDListItem -Label 'Autostart' -Nested -Icon (New-UDIcon -Icon Rocket -Size xs -Solid) -OnClick {
} -Style "
          .MuiSvgIcon-root {
             color: rgba(0, 0, 0, 0.6)

But I want to add it to my theme that I have on my dashboard page so it applies system wide.
And I have tried everything, I can get tit to work with MuiButton etc. but not the UDLIstItem.

@adam do you have some code for this? My guess is that I format the class under overrides wrong somehow.