This is a premium feature available with Astra Pro.
Make sure you have activated the module from Appearance > Astra > Addons > Spacing.
You can find settings under Appearance > Customize > Layout > Sidebar.
Below are the available options-
Sidebar Outside Space
This will add space around the widgets in the sidebar.
Topspacing value will add a margin at the top. Bottomspacing value will add a bottom margin for whole sidebar as well as the bottom margin for individual widget inside the sidebar.
- Left and Right space will add padding to the left and right side of the whole sidebar.
Sidebar Inside Space
It will add padding to the individual widget from all sides.