Styling Certain Widgets

I have a WP site with two sets of widgets. One section of widgets on the sidebar, another section of widgets on the footer. I want to put a styling per each widget, per each section. So the sidebar widgets would have a white background with 20px padding, while the footer sidebar widgets would have a green background and 40px padding. How do I manually insert these classes or code into the theme? Any help would be greatly appreciated.