This is a premium feature available with Astra Pro Addon plugin. To use these Pro features, you need to have the Astra theme along with the Astra Pro Addon installed on your website.
You can manage the spacing using the Spacing module available with Astra Pro. Please refer document, to begin with, Spacing module.
Make sure you have activated the module from Appearance > Astra Options > Spacing.
You can find settings under Appearance > Customize > Sidebar.
Below are the available options-
Sidebar Outside Space
This will add space around the widgets in the sidebar.
The top spacing value will add a margin at the top.The bottom spacing value will add a bottom margin for the 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.