While customizing your home page, this feature is available by using the Add section button.
Section style settings allow you to change the look of the section you are editing without changing the look of all the others.
You can change the style of many home page and product page sections across the site.
When you enable an Outline section setting, it removes the section background, letting your store’s global background color to show through. It then adds a border around the section, which uses your store’s border color setting.
For more information about color settings, see the Colors article.