From your Shopify admin go to your Theme > Customize > Theme settings > Custom CSS.
In the Custom CSS field shown you will need to enter the CSS to style the widget that you would like to style.
For each element you will need to target the element either by inspecting the element and / or using the ID of the widget. Below is a list of the IDs that you can use to select each widget you would like to style.
Widget | CSS selector ID |
Donations banner (product page) | #pledger-banner |
Customer donations | #customer_donations_widget |
Impact calculator | #pledger-impact-banner |
Once you have finished entering your styles into the Custom CSS field select [Save] (top right of screen) to save your custom CSS.