I would like the discount percentage % (circled in blue in the screenshot below) to have a green background color (#00FF00) and for the writing to be white.
From your Shopify admin dashboard, click on “Online Store” and then “Themes”.
Find the theme that you want to edit and click on “Actions” and then “Edit code”.
In the “Assets” folder, click on “base.css, style.css or theme.css” file, depending on which file your theme uses to store its CSS styles. At the bottom of the file, add the following CSS code: