In the "Box Settings" editor, there are two customization categories: "General" and "Look & Feel".
The settings we are interested in are located under the "Look & Feel" tab.
In the Box Settings menu, you will see a "Choose Box Style" dropdown.
Step 2 - change style
Click on the "Choose Box Style" dropdown.
In this dropdown, you have all the predefined styles in "Website Look & Feel -> Box Styles" as well as a "Custom Values" option. You can select one of the predefined styles or customize the box style by choosing "Custom Values" to style it exactly as you like.