Changing notebooks background globally

Questions
1

I want to set all the notebook background color LightGreen. I know I can use the command

Cell[StyleData[StyleDefinitions -> "Default.nb"], Background -> LightGreen]

in each notebook, but is there a better way that I can set it globally, such that when I open a new notebook the background will automatically become light green?

2

In the option inspector you can usually select the scope to be “global”. You could also edit the stylesheet directly.