I have a GP site at staging1.hardyness.com. On the Services | Group Exercise page, I have a sidebar with the GiveWP donation widget. I would like to make both the widget and green button under it full width and centered in the sidebar, and would like the sidebar contents to be centered on mobile.
You need to adjust the Padding of the Sidebar in Customizer > Layout > Sidebar to make it centered – you can adjust it separately for mobile by clicking the Mobile icon beside it.